The law is the law. They can't insist on appliances being fitted by a
club.
If that is their way then they should sell only through that club.

If they didn't sell it direct to you, they have no obligation to offer any
guarantee at all, so they can do what they like.

If it is dead in the box, it is the retailer that is liable, not the
manufacturer, unless the manufacturer voluntarily decides to offer a
guarantee, which may be more restrictive than the statutory rights you have
with the retailer and may include restrictions on who fits it.

Of course, most manufacturers offer relatively unrestrictive guarantees, as
otherwise the retailers would get very annoyed at having to deal with all
the issues and may delist the products in question.

Christian.