Hi Jim my name is Brian I think your problem is the ball cock in the tank, it can sound like the whole house is caving in sometimes, its called water hammer and the quickest way to repair it is to replace the ball valve.
Hope that helps
Hi brian, thanks for that, is this a difficult thing to do? could I do it myself or do I need to get a plumber in to do it?how much does a new ball cock/valve cost and how much should I be looking to pay a plumber to do this for me if I cannot do it myself.
A ballcock costs about £15.00 a plumber should be able to do it in 30 minutes, if your mains water turns off ok. You can do it without much of a problem. go into the loft lift the lid of the big tank you will see the ball valve go and buy one from B&Q or similar shop turn your mains water off and change it over its pretty basic stuff, just make sure you buy a half inch fibre tap connector washer aswell because they sometimes fall apart when you disconnect the pipe from the ball cock
Thanks and will do
Have a good evening