Hi Don

There are many kitchen cabinet makers throughout the uk, but I would
imagine they don't sell direct to the public.

White carcusses, tend to be associated with the diy stores you mention
and are often 15mm/16mm as oppose to the 18mm carcusses your are
looking for.

A really popular look at the moment is to have cabinets colour matched
with the doors and this is where the cabinet makers come in as they
basically custom build a kitchen to your specification. They buy the
doors in from another manufacture, be they solid wood, veneer or
vinly wrapped and will even add tandem drawer boxes and blum motion
fittings for a really superior kitchen.

However if you really wanted a white interior, you would need custom
end panels for the cabinets that are exposed. Again a manufacturer
could do this for you.

If you let me know what part of the country you live in I will see if
I can identify a supplier for you.

Regards Paul