Banging noise when certain taps run - Boilermate 2000

Hi,
I took ownership of a property in September 2009 which has a Gloworm Ultimate boiler in the kitchen and a Boilermate 2000 in one of the small bedrooms. Also a loft conversion was added to the property in 2007 with an en-suite. When in this en-suite and using the Cold Tap, or toilet flusha constant banging noise can be heard behind the walls which will carry on for a couple of minutes after the cold water tap has been closed.

Also, this banging noise will happen with certain other taps in the master bathroom. Using things like the washing machine and dishwasher on ground floor does not seem to cause this problem. I do not really understand the Boilermate 2000 system and have the Gloworm boiler set to maximum and just use the thermostat when needed for heating, which heats up within seconds (which was the extent of the previous owners instructions about the system).

Also, even if I leave the heating on e.g. 15 degrees overnight, I can hear my gloworm boiler coming on numerous times, so I'm sure this is costing me a fortune in Gas.

My main questions therefore are:

1. Has anyone got any ideas what the banging noises could be? I can even hear them in the middle of the night sometimes. I have been told it could be water hammer, but another plumber said water hammer only happens when water from taps has closed, not during flow.
2. Why does the Gloword boiler come on nemrous times, even when we seemingly are not using any water?
2. Can anyone recommened a good Boliermate engineer in the Milton Keynes area who could provide a healthcheck/service of the system to ensure I have it set up correctly/most efficiently? and to identify and fix any problems there may be? (I do have a British Gas servicecare contract and they said the system is running fine on their initial inspection visit they did, but I am not convinced on their engineers's analysis).

Many thanks in advance.
Joe