Any ideas ? Been told that it has an oil leak into the exhaust ? It clears when reved , but leave it idling and it returns . Engine seems in good health , with plenty of power .

blue colour?

The most likely cause is the turbo seals are shot.

Worth checking the oil return from the turbo isn't clogged before you splash out on turbo re-con.

The standard turbo on a 20vt Coupe uses pressure differential oil seals - when there's backpressure in the turbine housing (eg when the revs are up) there's enough pressure to make the seals, er, seal. However, at tickover, there's virtually zero backpressure, so the oil weeps past and burns in the exhaust stream

Refurb or replacement are the only options - it won't get better

The only possible cure is if the car is currently decatted, putting the cat back on *might* just create enough backpressure to slow down the oil getting past the seals, but its usually irreversible.

If the car is decatted and is going to stay that way, don't fit a standard turbo - the seals will fail quickly. You need an uprated turbo with better seals.