How much would a british gas combi boiler cost, supplied & fitted? are BG value for money?

There is no doubt that BGS will do a proper job. They usually install Worcester Bosch combis which are reliable boilers. As they do free estimates it would be wise to get them in and discuss the installation in detail. Then ask at least two other installers to quote. Checkatrade is one source of reasonably honest installers. If a quote comes in lower there is no reason not to ask BGS to match it. I use BGS for boiler maintenance and they are 100%.