With the growing strength of Parliament, more and more opposition was made to the grants of monopoly and their enforcement. In 1642 the House of Commons passed a resolution "affirming that the taking of the letters from the several carriers and the several restraints and imprisonments of Grover, Chapman, Cotton, and Mackerill are against the law." The House proceeded to state that these several persons should have reparation and damages from Coke, Windebank, and Witherings.[747] Four years later a report was made by Justices Pheasant and Rolls on Witherings' patent.[748] They held that the clause of restraint in the grant to Witherings was void.[749] This decision was quite in accordance with the views of Parliament when they opposed the King and all his works. But after Parliament had obtained control of the Posts, "the President and Governors of the Poor of the City of London" proposed to the Common Council that the City should establish a postal system in order to raise money for the relief of the poor in London. A committee was appointed to inform Warwick, Prideaux, and Witherings of their intention. At the same time an attempt to lay a petition before Parliament on the question failed. Counsel's advice was sought and obtained in favour of the undertaking and in 1650 the Committee received orders to settle the stages. At the end of six weeks they had established postal communications with Scotland and other places. Complaint was made to Parliament, and the Commons passed a resolution "that the office of Postmaster, inland and foreign, is and ought to be in the sole power and disposal of the Parliament." The same year the city posts were suppressed.[750]

Oxenbridge and his friends who had set up posts of their own gave Prideaux and Manley the hardest fight that any Postmaster-General ever had to encounter from interlopers. Joyce says that Oxenbridge had acted as Prideaux' deputy.[751] If this is so, he was soon up in arms against his superior. In accordance with the judicial decision that the clause in Witherings' patent giving him a monopoly of the carriage of letters was void, Oxenbridge, Blackwall, Thomson, and Malyn had undertaken the private conveyance of letters and had set up posts of their own. Prideaux had charged 6d. for each letter and had organized weekly posts from and to London. Oxenbridge charged only 3d. and his posts went from and to London three times a week. Prideaux then did the same and set up posters announcing that the interlopers' posts would be stopped. His agents assaulted Oxenbridge's servants and killed one of them. He also stopped his rival's mails on Sundays but allowed his own to proceed as on other days. In addition to his regular tri-weekly mails, Oxenbridge provided packet boats for Ireland and intended to settle stages between London and Yarmouth and the other places named by the Council of State.[752] To proceed in Oxenbridge's own words: "Suddenly contracts were called for. We offered £9100 a year through Ben Andrews, £800 more than was offered by Manley, yet Colonel Rich allowed Manley to take advantage of an offer made by Kendall then absent and not privy to it for £10,000 a year. Consideration had been offered by Council, but Manley had broken into our offices, taken letters, and had forbidden us from having anything to do with the post." An order of the Council of State, bearing the same date as the grant to Manley, was sent to Oxenbridge and his friends, informing them that Manley had been given the sole right to the inland and foreign letter offices.[753] This did not end the controversy, for six months later we find Oxenbridge and Thomson complaining that a monopoly in carrying letters had been given to Manley. They claimed that all who wished should be allowed to carry letters at the ordinary rates.[754]

Of all the interlopers up to the middle of the seventeenth century, Oxenbridge had proved himself by far the ablest. From the point of view of the legal decision of 1646 and the position of Parliament before 1640, his position was unassailable. With the present policy of the Post Office in view, his actions will probably be condemned by the majority. But in 1650 conditions were entirely different. Before 1635 the state had either tacitly allowed the carriage of private letters to the profit of the postmen or had officially taken over such carriage; but in this case it was largely for the purpose of keeping in touch with the plots of the times. For 200 years after 1635 the idea was to make money from the conveyance of private letters. The effects of Oxenbridge's efforts were certainly beneficial if we are to believe his own story. Prideaux had been forced to cut his rates in half in order to meet competition. The credit for this must lie with the interloper rather than with the monopolist.

At the same time that Oxenbridge was giving so much trouble, letters were being carried by private hands in Bury, Dover, and Norwich. The offenders were summoned before the council for contempt and severely reprimanded.[755] Petitions came from Thetford and Norwich complaining that their messenger had been summoned to present himself before the Council within twenty-four hours and had to travel 100 miles within that time, an impossibility in the opinion of the petitioners.[756] As late as 1635, Prideaux, the Attorney-General, gave his opinion that Parliament's monopolistic resolution of that year affected only the office of Postmaster-General and not the carrying of letters.[757] Perhaps this was only a bit of spite on his part after Manley had succeeded to his old position.

The usual monopolistic powers, hitherto granted by proclamation, were embodied in the first act of Parliament, establishing the postal system for England, Ireland, and Scotland in 1657. The Postmaster-General was given the sole power to take up, carry and convey all letters and packets from and to all parts of the Commonwealth and to any place beyond the seas where he might establish posts. He alone was to employ foot posts, horse posts, and packet boats. Some exceptions were made to these general rules. Letters were allowed to be conveyed by carriers so long as they were carried in their carts or on their pack-horses. The other exceptions were in the case of letters of advice sent by merchants in their ships and proceeding no farther than the ships themselves, and also in the case of a letter sent by a special messenger on the affairs of the sender, and in the case of a letter sent by a friend. Penalties were attached for disobedience to this part of the act, one half of the fine to go to the informer.[758] The same provisions were enacted almost word for word in the act of 1660, with the addition that letters might be carried by any one between any place and the nearest post road for delivery to the postman.[759]

After the restoration and for some months before the act of 1660 was passed, Bishop had acted as farmer of the posts. In the absence of any law on the subject, the King's proclamation granting a monopoly[760] to Bishop was freely disregarded.[761] Competing posts to and from London sprang up, lessening the receipts which he would otherwise have obtained from the carriage of letters. It was calculated that during the three months before these interlopers could be suppressed Bishop lost £500 through them, and orders were given to allow him an abatement in his rent to that amount.[762]

In 1663 a certain Thomas Ibson attempted to come to an agreement with the postmasters on the Holyhead road. He wished to have the privilege of horsing travellers and made an offer to the postmasters to take charge of the post houses if they would allow him to proceed. He told them that they should make an attempt to have their salaries restored to their old value by Bishop, who had raised so much from them by fines and lowering their salaries. The Postmaster-General told his deputies that if they dared to treat with the "would-be" interloper he would dismiss them, and the whole thing fell through.[763] At the same time a warrant was issued by the Council to mayors and other officials to search for and apprehend all persons carrying letters for hire, without licence from the Postmaster-General.[764] Nevertheless interloping did not cease, as is shown by the complaints from the postmasters.[765]

In the proclamation following the appointment of O'Neale as Postmaster-General in 1663, it was ordered that no one should dare to detain or open a letter not addressed to himself unless under a warrant from one of the Secretaries of State. An exception was made in the case of letters carried by unauthorized persons. Such letters should be seized and sent to the Privy Council. In later proclamations it was provided that they might be sent also to one of the Secretaries of State in order that the persons sending or conveying them might be punished.[766]

After Lord Arlington's appointment as Postmaster-General, he addressed a petition to the Duke of York complaining "that carriers, proprietors of stage coaches and others take upon themselves to collect letters to an incredible number and on some stages double what the post brings." On account of this he pointed out to His Royal Highness that a considerable part of his revenue was lost. This was quite true since the Post Office had ceased to be farmed and the whole net revenue went to the Duke.[767] This was followed the same year by a proclamation forbidding any one to collect or carry letters without the authority of the Postmasters-General. Carriers were forbidden to convey any letters which were not on matters relating to goods in their carts. Shipmasters must carry no letters beyond the first stage after their arrival in England with the exception of the letters of merchants and owners. Searchers were appointed to see that the proclamation was enforced.[768] It was even proposed to suppress all hackney coaches, the principal reason given being that they decreased the value of the Duke's monopoly by carrying multitudes of letters.[769]