Muskrat. No, the oil tank was not topped up, I have an isolation tap on the oil feed pipe, which is turned off when the bike is in the shed, the timing cover was removed to re-gasket due to slight leak, so there is two things to my mind, as you say cork on the timed breather too thin or, obstruction in the scavenger pump. I will be working on it today all being well and hope I can find out the answer but it's always good to hear other members opinions and I do value these, many thanks.
Regards TTJohn