Both cheap and poor quality, in my opinion - especially TM Lewin.

I've recently gone for bespoke with Turnbull & Asser. Not the cheapest but absolutely outstanding quality and service.

They are also better than other bespoke or made to measure shirtmakers I've tried in the past, as they make you a test shirt based on your measurements which you then wear/wash/iron for a while which they then use to ensure your actual batch of shirts fits perfectly.

Edit - if you are mail ordering rather than visiting in person you might want to give Thomas Pink a look. I have also heard good things about these guys http://www.barringtonayre.co.uk/shirts/ - although I have not tried them myself.