Gassing - ECU help Please

[speed.demon]

I need to find a resemble priced but good engine tuner, who can port my engine and adjust my ECU as I understand this is where most of the gain can be made?
(in colchester essex area would be a bonus)

Can you advise me on who to phone / web address

and what gains should i be looking at??

I have a Citroen 1.6 16V GT to tune.......

Regards

Speed.Demon