Omnimount are known for being one of the market leaders in TV wall brackets. The LIFT 50 is their model suitable for 40"-50" TVs.
This model was £299 not long ago. Cheapest on eBay new is £288.29. Currys dropped price to £169.97, and have now dropped a further £10 off for the last remaining few. Go through Quidco for further 5% off.
Full manufacturers details & demo video here: http://www.omnimount.co.uk/products/tv_wall_mounts/interactive/lift50/