Lizard Trailer Services of Helston, Cornwall. VERY competetive. 01326 563282. My son recently bought one from them that was £100 cheaper than elsewhere local.
There's a company called Admiral based in Tiverton, try a Google search. They seem keenly priced but suggest you haggle, the price they quoted me was the same as I got from one of their dealers.
Bramber also make excellent trailers, I bought one from them years ago when they were in Willand, don't know if they're still there.
Try Parrymore Trailers too. They have an interesting design that allows the axle(s) to be moved fore and aft for reasons of balance ... and are competatively priced. Good Luck
Bought twin axle 2500B for near a GRAND less than any other manufacturer,even better spec & built for the actual boat.
This involved extra length to the draw bar which was not explained by other manufacturers (Boat has anchor platform) .
Owned now for 4 years & has approx 2000 miles with no defects.
20-30 saltwater dips still going strong with no corrosion.
Has full mail order spares dept (lost detachable winch handle once) which was posted out even though they were closed for buisness one late friday evening.