What was lord Grenville's plane to enforce new taxes

There was opposition to the Revenue Act of 1763, on a basis that no one in Parliament could have foreseen.

The Revenue Act, which came to be called the Sugar Act, was actually an extension of an act from 1733 called the Molasses Act. The Molasses Act required a tariff on all sugar products that were imported into America from the West Indies. The American colonists, however, had found that it was not difficult to smuggle their sugar items into the colonies and avoid the tariff that was due to the British government. This sort of activity was not allowed to go on in any other part of the British Empire, and Lord Grenville saw no reason why it should be permitted in the colonies and be winked at by England.