So after trying a few different places here are the suppliers I use for different materials.
Amazon.co.uk for 3mm laser MDF in A4 or A3 sheets - great stuff, very consistent. All my designs are done to fit one or the other of these sheets.
Also some assorted bits of A4 acrylic.
Hobarts.com for acrylic. I buy the 450 x 300 sheets (just fractionally larger than an A3). Just be careful that when choosing you check the finish, they have a mix of frosted and opaque.
I am in love with their “glass green” acrylic.
Kiktronic.com for other acrylic. I’ve bought some A4 sheets, mostly for things not available at Hobarts.
Ebay.co.uk for leather “scraps”. I bought one of the big bundles of leather scraps. They are left-overs from furniture makers, not delicate stuff, but a good mix of medium and heavy duty. Sizes are quite large.
I’ve also bought assorted bits of veneer and 2mm mahogany and bamboo, but not so keen on those.
Farnell.com for the 3M Degreaser at a reasonable price.
Any other suggestions and recommendations?