A number of British formations used turret numbers in NW Europe; chiefly 79th Armoured Division, and 27th and 33rd Armoured Brigades.
These numbers were typically very large and somewhat crude looking; apparently being hand-painted rather than stencilled. As a result of this they may not be a perfect match for your chosen regiment, but the style of numbers used has been based on photos, predominantly of 27th Armoured Brigade Shermans. The most common variety of these was in red with a narrow white border; this sheet provides numbers 01 - 40 in this style.
Numbering systems varied, but usually 01-20 were the HQ and 21-40 "A" Squadron - numbering wasn't continuous, so if "A" Squadron had 18 tanks, they'd likely be 21-38, with "B" Squadron starting at 41 regardless. In some units the numbering started one earlier, so the squadron HQ vehicles may be 20, 40 and 60 rather than 21, 41 and 61.