Acer Aspire 8920G-6A4G32Bn, with Intel Core 2 Duo T5750 2.0GHz Processor, 18.4" 1920x1080 Screen, Vista Home Premium, 4GB RAM, 320GB HDD, Blu-Ray reader, NVidia Geforce 9500 Graphics £649.49
Yes, that's quite a heavy machine at 4.1 Kg but it is a great spec for the price!
Look out if you search the net for comparisons and reviews - there are at least 4 models of the 8920g!
This one has the full 1920x1080 screen for 1080 resolution Blu-ray playback.
There is a slightly cheaper model (about £25 less) called the 8920G-6A3G25Bn - but that only has a 1680 x 945 resolution screen as well as less RAM and disk!
Also, this is NOT the model with the TV tuner and remote control. That will cost you another £350: http://www.simplyacer.com/Acer_Aspire_8920G-934G50Bn_412003.html
but you also get a faster processor and more disk with the more expensive one.
If you believe in buying warranties (personally I don't) there is a 3 year "collect and return" warranty for £50: http://www.simplyacer.com/Acer_Gold_3_Year_Collect__Return_Notebo_461404.html
or a 3 year warranty plus accidental damage cover for £90: http://www.simplyacer.com/Acer_Platinum_3_Year_Collect__Return_Wa_461405.html