I dunno how Roccat Ryos MK advance costs in UK but that is the cheapest you can find with Macro keys and backlight. One thing to notice, it has only the Cherry MX black version, if you want to have the red or blue or brown, well, you must look else where (costs more).
You can also find QPad MK-80 pro below £100 once in a while on special sales, but that one does not have macro keys (if I understood it correctly)