For carpets I go to Carpet Right. Good carpets cost from �10 sqm to �70 sqm then underlay �3 sqm.
Laminate �7 sqm
http://www.carpetright.co.uk/pages/at_home/def ault.aspx
Plastering, how many walls approx how many sqm ?
What type of lock and door do you have?
Wooden door, UPVC?
What type of lock? rim lock, mortice ?
Gas fitter, is there an existing fire or is it a new installation?
With an existing fire you'll probably have a flue liner already if not it'll cost more to have one fitted.
All these trades can be found in your Yellow pages or Thomson local directory.