A painting that may be the only surviving portrait of William Shakespeare made in his lifetime will be unveiled.

The picture, from 1610, six years before the playwright's death, has been in the possession of the Cobbe family since the early 18th century.

It was initially kept at a property in Hampshire but more recently in Hatchlands, the family house in Surrey, which is run by the National Trust.

For three centuries the family was unsure of the identity of the figure in the portrait. According to Alec Cobbe, an art restorer, at one time it had been thought to be of Sir Walter Raleigh.

Although the painting has not been proven to be the bard, it has the backing of the world's foremost expert on Shakespeare, Stanley Wells, emeritus professor of Shakespeare studies at Birmingham University and chairman of the Shakespeare Birthday Trust.

Prof Wells believes it was painted when the writer was 46 years old, six years before his death in 1616.

The portrait is thought to have belonged initially to the third Earl of Southampton, who was Shakespeare's patron.

Meanwhile, enthusiasts also claim to have unearthed new works by 'Shakespeare' after 400 years.

John Casson supports the thesis first mooted in 2005 that an Elizabethan diplomat named Sir Henry Neville was the real author of William Shakespeare's plays.

Dr Casson, in his book Enter Pursued by a Bear, identifies 'Shakespeare's' first published poem as the 'Phaeton sonnet', his first comedy as 'Mucedorus' and 'Locrine and Arden of Faversham' as the first of the tragedies. All of these were created ten years before the Henry IV plays.

"After 400 years we can now see 'Shakespeare's' early artistic development. What we thought were the first plays by 'Shakespeare' appeared anonymously in the early 1590s. It is inconceivable however that his first plays were the massive trilogy of Henry VI. Writers develop over time from simpler beginnings. I have discovered some of those earlier writings," he said.

The findings have been welcomed by leading actor Sir Derek Jacobi. Sir Derek said: "I consider it to be a work of first class research and scholarship, full of fascinating indicators all pointing away from the orthodox belief."