On the back cover of Peter's book, he quotes from a speech from Lord Annan on the Broadcast bill 1990, here is a bit more & a link to the source:

I particularly dislike the extraordinary amendments to the marine broadcasting Act 1967 which are aimed at Radio Caroline. The amendments proposed will make it unlawful for any foreign ship on the high seas to broadcast to the United Kingdom. It will enable the police, the army, Customs officers and anyone who is authorised by the Secretary of State to board and search these foreign ships and to seize documents.

Is this not another example of the Government putting on their Clause 28 "bovver boots"? Exceptional cases such as highjacking or drugs could justify seizure or detention of a foreign vessel and confer immunity on the officers who boarded it. I realise that the Home Office regards Radio Caroline as a maddening wasp and is infuriated that its attempts over the years to swat it have failed. However, surely this station is not a wasp but a common or garden cabbage white. Why break a butterfly upon the wheel? Why run the risk of an embarrassing diplomatic confrontation? That could perfectly well happen if the vessel turned out to be under an American flag.

https://api.parliament.uk/historic-hansard/lords/1990/jun/05/broadcasting-bill#S5LV0519P0_19900605_HOL_100