THE 200th anniversary of the birth of Robert Stephenson was yesterday marked with a string of ceremonies - and news of tests that are due to find out whether he was a drug addict.

Tests on a lock of hair taken from one of Britain's greatest engineers will examine whether he was a drug addict who may have died of mercury poisoning. Stephenson built the famed Rocket locomotive with his father, George.

A lock of his hair is believed to have been taken at the time of his death in 1859 and is on display at the National Railway Museum in York.

A sample has been given to forensic experts. Contemporary reports say he often turned to drugs to escape the pressures of work.

Scientists will be looking for traces of opium, the fashionable narcotic of the time, and evidence of mercuric chloride - a toxic compound administered by Victorian doctors as a purgative in the treatment of ailments.

Yesterday, commemorative plaques were unveiled at Stephenson's workshop, in South Street, Newcastle, and at the Literary and Philosophical Society in the city's Westgate Road, where he was president.

Robert Stephenson began his career by helping his father around Tyneside constructing colliery railways. They co-founded the world's first purpose-built locomotive factory in Newcastle.

This was the beginning of steam locomotive development and birthplace of the world-famous Rockets.

In 1825, they built the world's first public railway - the Stockton and Darlington.

Robert Stephenson was also responsible for the Newcastle High Level Bridge, opened in 1849, and the Royal Border Bridge in Berwick, which opened in 1850.

An exhibition celebrating the bicentenary of his birth runs at the Newcastle's Discovery Museum until November 23.

The renovation of Stephenson's original workshop, in South Street, is near to completion and will open as an archive and display centre for Stephenson's work next year.

The workshop will be open to the public from 11am to 3pm on Sundays.