clicking? kinda like metal pinging sounds of detonation?

Detonation occurs at high temperatures, so it could explain why the car "runs" fine when cold.

If you're tech savvy, I'd say take off the head and check for damage, see if the pistons have been banging against the valves or if the pistons seem damaged. If you're not tech savvy, I'd take the car to a skilled mechanic.

Detonation occurs when the heat and compression of the fuel when the piston is at top dead center, and has just started burning the fuel, the heat and compression make the fuel suddenly detonate, instead of burning normally. This sort of engine problem is usually caused by too much boost, too hot air, too high compression in the engine, and/or too low octane fuel.

A fuels octane rating is its resistance to detonation, which is why turbo cars, should always run high quality fuel. What kind of fuel have you been running (and please say the octane numbers, since I'm not familiar with the fuel brand names in the UK )

Oh, and here is a sound rule-of-thumb I got from Maximum Boost, "If you hear pinging or knocking, step off the throttle NOW!" (Ok, I may have worded it differently, but in essence its the same).

Anyway, _NOTHING_ can withstand repeated detonation shockwaves, and this pinging/clicking sound you hear might be that.. An engine which is running at 3000 rpm, will be detonating 50 times per second!