What's the burning smell from my Britannia dual fuel range cooker?

We've had the 100cm model for over 2 years (so out of warranty now).

Despite cleaning & removal of cleaning deposit , the Large l/h electric oven has started emitting light smoke which smells like burning plastic or rubber. Small flumes can be seen coming out of front just under hob. No sign of anytbing burning inside. is there an internal part inside that needs replacing?