You have a water imbalance in terms of pressure. Usually, the cold has more pressure than the other. Both should be equal at around 2 bar minimum. The correct way is the purchase of a PEV valve (pressure equalising valve) and these are about £70.00.

What is a pressure equalising valve (PEV)?

What we would suggest FIRST is buying 2 x water shut-off valves if not already installed (as they should have been) and putting these in line on the hot and cold then just turn one down. Start with cold, and see how you get on. May need to play with them a bit. Only around £5.00 for a pair at B+Q or screwfix. This is almost certain to cure.