BG don't charge for their check it is included in the maintenance contract.
BG started with the analyser "service" about 15 or so years ago. Part of their 3 star cover was to include an annual service. As we all know balanced flued boilers generally are normally pretty clean inside, so they decided it was a waste of manpower to have someone actually strip it down. Much quicker and cost effective to "check" if it really needed servicing. So their included service really became a check. All the major contract providers are the same.
Now analysers are commonplace and actually opening a band A is only advised if the readings say so, this practice has become the norm for all boilers. Its should be called as it is though, a combustion check which is totally different from a service.
An analyser it not necessary or required to service a std boiler but it is another tool to use as part of one. You don't need to own or have access to one either, just be able to interpret the results.
Btw, anyone who sticks an analyser in an open flue boiler as an annual check and accepts the readings as being fine is off their head.