There was, however, one element of weakness in the position of the United Provinces on which the English were never weary of insisting. By his possession of the cautionary towns the King of England appeared in the eyes of the world to be recognized as a protector of the Dutch Republic, who had certain rights over it. Oldenbarneveldt in his negotiations had doubtless been hampered by the plain evidence which the presence of English garrisons in Flushing, Brill, and Rammekens afforded, that the States did not exercise full sovereign authority within their own borders. In these circumstances he (Oldenbarneveldt) knowing full well the financial straits to which King James was reduced through the long-standing disagreement between him and his Parliament, made overtures in 1615 through the resident ambassador Caron to redeem the towns by the payment of a sum of ready money. The annual charge of £40,000 received from the States was barely more than sufficient for the maintenance of the garrisons. The total amount claimed by the English Government was £600,000; the Dutch offered £100,000 in cash, and three further sums of £50,000 in half-yearly instalments, or £250,000 in all. The offer was accepted and in June, 1616, the cautionary towns were transferred into the hands of the Dutch.
It was, however, agreed that, for the sake of maintaining good relations between the two countries, the new English ambassador, Sir Dudley Carleton, should like his predecessor, Sir Ralph Winwood, retain his seat in the Council of State. This was the more important, as the King had (as already stated) for the past three years been steadily moving towards a Spanish alliance. What were his precise aims and what his ultimate purpose it was difficult even for the practised and penetrating insight of a statesman of Oldenbarneveldt's experience to discover. Perhaps James scarcely knew himself. But the retention of fortresses like Flushing and Brill at the mouths of two most important Dutch waterways by a foreign sovereign, who was intriguing to win the favour of the Spanish foe, was for the Republic a most serious danger. Their redemption therefore at so trifling a cost was a stroke of policy by which the aged Advocate did a great service to his country. Certain it is that James felt a grudge against Oldenbarneveldt, and that, when shortly afterwards civil strife broke out in the United Provinces, Sir D. Carleton, acting on the King's instructions, did his utmost to bring about the great statesman's downfall and to support his enemies in compassing his death.