[vidarh]

I can't find anything to support the claim that they require a prescription from any authoritative source. The page you reference cites guidelines from an association that has no legal power. The relevant Act seems to only define a prescription regime for medication, and to only specify category classifications for medical devices for the purpose of certification, not restrictions on purchase. But I'm not a lawyer.

Which law is it you think Amazon would be breaking?

EDIT: In fact the page you linked itself points out that the "prescription" they are talking about is in fact not a prescription. "When the word 'prescription' is used for the purchase or rental of a CPAP machine, this is not like a standard prescription which GP's provide for medication."