'Pipe Hammer'

I have a totally new system (pipes boiler radiators) when I turn off the tap I get a hammering noise on the old and new taps. I've reduced the flow in to the house and at the tap which helps but doesn't eliminate it. I can't reduce the flow too much because then there is too little water.
Any suggestions appreciated

Two possibilities.
1. Air in pipes. I find turning on each tap in turn for a while will cure this. Usually it is near pipe end supplying an en-suite .
2. High mains pressure causes attic cold tank ballcock to oscillate as standing wave setup by water coming in. Either reduce flow to tank or guide inflow so no waves occur.

Let us know how you get on!

I have left the taps running for several mins at a time and still no joy.
Reducing the flow in to the house helps but then if I turn the tap on in the bathroom in reduced the flow in the kitchen so it's a balancing act.
There is no cold tank, it's a new system with a combi boiler.

Agree you should not reduce inflow to house. Water hammering occurs when flow abruptly cycles from halting to starting. I have only seen it caused by air in pipes or ballcock valves. With no cold tank that only leaves toilet cisterns suspect. I would tie these up so no inflow can happen and see if water hammering stopped.
If water hammering still occurs you must have air trapped somewhere in my view. Who did your plumbing? They may have incorrectly routed piping so air is help. However I am puzzled as at mains pressure all air should be forced out!