notafish, As usual, Albags is on the mark.
Previous to taking early retirement, I used to specify gas boilers for a large local authority. Following installations and monitoring of various boilers, Worcester Bosch ( WB ) always proved to be best.
Consequently, they were specified, providing the budget would allow it ( WB are one of the dearest boilers on the market ).
However, the Inter Gas boiler ( formerly Atmos boiler ), is attaining very good reports ( check various heating installer forums i.e. 'diynot.com' ).
Re your points of concern, Reliability : As these boilers are both top of the range, the reliability should be very good ( check the manufacturers guarantee, they tend to differ ). Value for money : as usual, you get what you pay for. ( you want the boiler to last at least ten years ). Safety : All boiler manufacturers must adhere to stringent tests regarding their appliances before they can be marketed. Your installer should ensure that the gas supply is safe, and commission the boiler. ( ensure your installer is 'GAS SAFE' registered. Economical to run : All new condensing boilers are much more economical than older standard boilers .
Some heating engineers tend to 'push' a certain boiler as they get a bigger discount from their supplier.
The choice between these two top of the range boilers in the end will be yours.
Hope this helps.