I would 100% recommend the CAA/ASG M4, it's been brilliant for me and is only £129.99, you will have to purchase the downgrade to make it site legal but it's well worth it!
http://www.patrolbase.co.uk/airsoft-m4-m15-m16-variants/asg-caa-m4-sl-series-cqb-two-tone-blue.htm#.WFm5iIHfWEc