Need some help, my car seems to be using a bit of water. It overheated yesterday. I've had a new rad cap and thermostat fitted, also had the sniff test done which was all clear. Could this be the water pump that's knacked or radiator

I would be looking for a water leak on the pipework somewhere or as you say Radiator , Its unusual for waterpumps to go wrong on L200's ( not unheard of, but unusual! )
It will only take a small hole to lose water ..are your heaters still running hot , and just check you haven't a damp carpet...

Have you recently had any work done on it?
Does it have excessive ' white ' smoke from the exhaust?

I've had new timing belt done..new thermostat ..full flush..heater works as it should and temp gauge always reads half way. No wet carpet.

Has it only lost water since you had the belt and thermostat done?

is the rad cap the correct one ? only ask as the pressure will affect the boiling point considerably