But much more than the Navigation Act, some other proceedings of the Parliament increased the tension between the two countries. In November they renewed certain letters of reprisal against the Dutch, under which a few of their vessels were captured. More serious were the actions of English men-of-war and of some privateers who held letters of reprisal against the French. An informal maritime war with France began in 1649 and continued till 1655, and though there was nominally peace, the English captured French vessels, and _vice versâ_. They then began to seize Dutch ships, suspected of having French goods on board, and brought them into English ports for trial in the Admiralty Court. This was an interference with freedom of commerce which the States could not tolerate, and an embassy to England, which had been decided upon after St John left The Hague, was despatched thither.[700] The three ambassadors, Cats, Schaep, and van de Perre, arrived in London on 15th December 1651. They were instructed to renew negotiations for a treaty on the basis of the thirty-six articles, to endeavour to get the Navigation Act repealed, the captured vessels released, and the letters of reprisal withdrawn, with compensation for the losses suffered by reason of them. The question of adding another article to their instructions, about the striking of the flag, which had been omitted from the thirty-six articles, had again been considered. But, for the same reason as before, it was withheld. “The carrying or striking of the flags by the one side or the other” was judged to be “very delicate”; and it was decided (on 10th November 1651) that the States-General should deliberate further on the matter, and send later to the ambassadors such instructions “as should be found suitable for the removal of misunderstandings and hostilities.”[701] We thus see that in 1651 the Government of the United Provinces was fully alive to the risks and difficulties about the flag. But from their proceedings at this time it would seem that they were unwilling to acknowledge unreservedly the claim of the Commonwealth to the salute, which was looked upon as a symbol of England’s sovereignty of the sea. The question was only rendered “delicate” because of certain qualifications and conditions of reciprocity which they desired to attach to it, and for which they struggled hard with Cromwell during the subsequent negotiations for peace.