Hondata is gonna be the best ECU for your application, be prepared to pay around £500 for the unit itself and then £3-500 for tuning.
I haven't looked much into tuners round London (even though that's where I live) as there's only one tuner I'll be going to when the time comes: EK9Turbo. He's a user on this forum, give him a PM if you want to discuss prices/details further...