An HD 6750 requires a 450W PSU with at least 26A on the 12V rails and one 75W 6-pin PCIe power connector. Total power rating (watts) on the PSU is not the most important factor in selecting the PSU, total amperage available on the 12V rail is more important.
The Antec VP350 with 28 A on the 12V rail and one 75W 6-pin PCIe power connector is sufficient for your build. http://www.scan.co.uk/products/350w-psu-antec-basiq-vp-350p-gb-90-eff-120mm-fan-atx-v23#ProductFeatures
at 25.62 which is slightly less than at ebuyer: http://www.ebuyer.com/278493-antec-vp-350w-psu-0-761345-06431-6