They have to be fit for purpose, and it looks like they fail that test.
Be wary of this – “fit for purpose” is the lowest possible qualification, as far as I understand it. The example I was given by a Trading Standards employee, also a cyclist:
If you want a cross-country mountain bike and I sell you a hybrid commuter, or even a Brompton, that fulfils the legal qualification of “fit for purpose”. Because you can ride it as a bike. Even cross country, even if only briefly.
If you want a cross-country mountain bike and I sell you a bucket, _then_ can you argue that what I sold you is not “fit for purpose”. There are many other levels of recourse before you get to “it doesn’t fulfil even the most basic interpretation of its purpose.”