Screwfix are generally very good and I have ordered quite a lot from
them. They once supplied a faulty consumer unit and replaced it with
another faulty consumer unit, but apart from that, I have not had any
problems.

My orders are usually small and my only complaint is the amount of
packaging they use. After every delivery, there is masses of cardboard
and 3 or 4 of those annoying bags of air to throw away!