Manky Monkey Motors

Is leather best for cover? Any upholsterers recommended in Essex?

Depends what kind of use you plan Rod. I've had real leather bike seats in the past. If the bke's used all Winter in rain & snow n stuff, the leather eventually goes white & furry. If it gets left out all Summer in hot sunshine it can go rock hard or crack. Using a good saddle soap, (used for protecting horse sadlles), should keep it in good condition.
Vinyl's usually much cheaper, easier to get hold of & these days, often hard to tell from real leather. It also comes in a variety of patterns. I had the seat on my last trike recoverd several times. The last cover was made up by a local guy in Basingstoke, Hants, using inserts in dimpled vinyl, (like the surface of a golf ball). There's a few names in the Links for commercial purposes section of the forum. Always happy to add more if you have anyone you'd recommend.