Byline: Steven Henry
IT is a simple demonstration sketch of Jack Vettriano's most famous painting.
But even this rough and ready copy of The Singing Butler by the artist himself is testament to his considerable cachet after it sold for ?39,650 last night.
The work was dashed off in just an hour when Vettriano gave a masterclass to students at St Andrews University in 2003.
After presenting the university the sketch, he then gave students his blessing to auction it for charity.
It was expected to raise ?20,000 but surpassed all hopes when it finally came under the hammer at the Sotheby's sale in Gleneagles.
'We are absolutely …