I use this company:
e-mail:
info@dezigned4u.comTelephone 01291 423724
The name of the guy is Paul Hardy; a friendly chap.
It's in Caldicot, just outside of Chepstow; they also sell on e-bay and will post your gear out.
I paid 7.50 per polo shirt and we bought about ten of them. Each of these shirts have my company name and telephone number on the back of them; similar to the polo shirts worn by staff who work in Wilkinsons.
Paul will advise you of a colour scheme for the effect your after (such as just a layout for 'customer branding' or one for 'high-impact noticeability') and the kit he provides is top notch.
I don't think they have a minimum order either.
Tell him, 'Tosh from ABC Window Cleaning' reccommended him and I might get a free fleece with my next order!