If you search this forum there are a lot of other threads on the subject. I have a lenovo thinkpad W520, with 16gb ram and quadro 1000m with an i7 processor. Seems to work pretty good.
£500-700 will get you a Dell Pro M6600 with ATI graphics and with the I7 and 8Gb ram that runs even my big assemblies with ease.
Solidworks 2013 64 sp1
I have a 3 year old MacBook Pro that i like very much but it did not like win 7 with solid works.
I wish i could of used it but wit 2013 solid works program that is very powerfull.
Thanks for the tip on Dell pro m6600
I will give that a look.