Who offered the colonists a conciliatory proposal which allowed the assemblies to levy taxes on their colonies upon the demand of Parliament?

This proposal was offered by Lord North, the Prime Minister of Great Britain. It was, as described in the question, essentially a compromise proposal, but it did not address the core grievance of the colonists, which was that they were being taxed without their consent. After all, if their assemblies failed to vote for a "contribution," Parliament would still be able to levy taxes against them. It was designed to appeal to moderates and conservatives in the colonies, which were by then in various stages of rebellion. North also hoped that perhaps some of the colonies would approve the measure, thus separating them from the radicals in New England. The Continental Congress, led by the delegates from Virginia (whose response was written by Thomas Jefferson) rejected the proposal outright, and the Olive Branch Petition, sent to King George at about the same time, failed to get a response from the King.