You cannot go wrong down Jermyn St, most if not all the shirt makers there offer MTM and bespoke to suit most budgets. I am a Turnbull man although quite pricey for bespoke the fit is perfect for me and finest quality.
If i saw a pair of John Lobbs for Â£100 and were half a size bigger then damn yes i would buy them... otherwise never..for my feet a half size bigger makes a difference a big difference. They may fit OK for the first few days but after a short while my feet will be sliding all over the place!!