So flat out in 2nd

valves going like the clappers and smoke. Your valve guide seals are worn and letting oil pass into the cylinder. Also your rings will be worn and letting bit more oil into the cylinders too and on ignition the oil is burnt off.
It should be using oil!
It could also be head gasket. As the revs are up and pressure a the coolant could be passing the gasket into the cylinder.
Was it white smoke or blue?
If you leave the car off for a few hours and start it does it kick a bit of smoke out? Try standing at the door and start it with foot on the throttle and see if theres smoke.