Sir David will still undergo checks

He said: "It was a routine blood test by my GP which showed I had prostate cancer.

"Naturally I was pole axed. If he had not done that I would not have known anything was wrong.

"In due course I could have become ill but it might have been too late by then."

Sir David was given the all-clear to return to full-time work by doctors at Edinburgh's Western Infirmary on Thursday following successful radiotherapy treatment.

He said: "The moral of the story is that routine testing for men over 50 is very important."

The most recent figures from 1997 showed that 1,800 men were diagnosed with prostate cancer in Scotland that year and 760 died from the disease.

Sir David said he was keen to work with prostate cancer charities to raise funds and help people with the condition get the right support.

'Public education'

He said: "I am so grateful to all the people involved in my treatment. I feel I owe it to them.

"The least I can do is help improve public education on the issue."

The former Liberal Party leader said he found it "annoying" to have to cut back on official duties while he underwent radiotherapy which left him feeling exhausted.

He said: "I felt completely washed out which was very strange for me as I have never really suffered any ill health in my life."

Despite being given a clean bill of health Sir David still has to have check-ups every three months for the next couple of years.

He still intends to step down as Presiding Officer in May 2003 at the Scottish Parliamentary Elections.