Small local BM’s are OK but avoid the large national chains as they will charge you extortionate prices, along with that well known national tile stockist; can be robbing, thieving bsatrds unless you seriously haggle. Local CTD as JCT says; unfortunately mine closed down & went back to Ipswich about a year ago . B&Q trade stores can be surprisingly reasonably priced for some building materials; plaster products in particular & they now stock Mapei I believe but unsure to what extent.