Haven't heard that it's a legal raquirement but agree with tribalelder that anyony who ventures out without a VHF is foolish.
Careful about buying from USA - they have different channel allocations to elsewhere in the world. Suggest you buy from UK or Turkey.
If your boat has a UK flag the boat will need a radio licence (Now free and available on the internet) and you will also need an Operator's Licence which involves a short course and exam.