The rate for a single letter, which had been raised by Prideaux to 6d., was in 1655 or 1656 reduced to 3d., owing to the efforts and competition of Clement Oxenbridge and others, who established and maintained rival services for the carriage of letters. These "interlopers" received scant consideration from Prideaux, and the services which they had established were suppressed.[36] In 1657 an Ordinance of the Commonwealth Parliament further reduced the rate to 2d. for a single letter sent for distances under 80 miles, and 3d. for distances over 80 miles. The rates were not, however, as low as would appear at first sight. There is the difference in the value of money to be allowed for; and there is the further consideration that postage was not charged according to the direct distance. All the post roads converged on London, and there were no cross posts. All letters from towns on one post road for towns on another post road must therefore pass through London, and all letters passing through London were subjected to an additional rate of postage;[37] that is to say, they were charged the appropriate rate in respect of the distance to London, and then, in addition, the appropriate rate in respect of the distance from London to destination. The Ordinance of 1657 placed the Post Office system for the first time on a statutory basis.[38] The objects for which such an Office was required were given as three in number: first, to maintain certain intercourse of trade and commerce; secondly, to convey public despatches; and thirdly, to discover and prevent many dangerous and wicked designs against the peace and welfare of the Commonwealth. In 1660 an Act of Parliament was passed, dealing with the Post Office.[39] Essentially it was the Ordinance of 1657, passed as an Act to give it legal validity under the changed order of things. The clauses relating to the use of the Post Office as a means of detecting plots against the State were included in a modified form, and this function was by no means lost sight of.[40] During the excitement caused by the Popish Plot it was freely exercised. The general farm of the posts was abolished in 1677, and the administration of the Office undertaken by the Government, except in the case of the smaller branch posts, in regard to which the practice of farming was even extended in the early years of the eighteenth century.[41] The revenue yielded by the Office continued to expand. In 1694 it had reached £60,000; and when, for various reasons, but chiefly to provide for the control of the Post Office in Scotland, which had been brought under the English authorities by the Act of Union, a new Post Office Act became necessary, the Ministers, involved in a protracted war, seized the opportunity to obtain an increased revenue from the Office. Under William III this had been thought of.[42]