Some UK suppliers that I have used, apart from technobotsonline. I cannot comment on returns as I have never had to do so.
My favourite from the list is hobbytronics as they have given me superb service every time I have ordered from them. I also order quite a bit of stuff from eBay and have a few shops/sellers that I return to as there service is also good and cheap.
For some larger projects I order components from Mouser, CPC & RS but you have to remember the prices are not VAT inclusive.
http://www.coolcomponents.co.uk/catalog/
http://hobbycomponents.com/index.php/