Award-winning performer Richard Griffiths, who appeared as Uncle Vernon Dursley in Harry Potter films, was hailed as one of the greatest and most-loved British actors by a string of his co-stars and colleagues.

Richard Griffiths, who had struggled with declining health in recent years, is thought to have been admitted to hospital for a heart bypass.

A friend said: “He had the operation, came out of it and there were massive complications. His heart and body gave way. He had had myriad health problems over the last five years and in the last three to four months he was getting increasingly breathless.”

Richard Griffiths was also best known for his role as inspirational teacher Hector in Alan Bennett’s The History Boys – which earned him a Laurence Olivier award – and for playing Uncle Monty in cult film Withnail & I.

The actor was awarded an OBE for services to drama in 2008. Harry Potter star Daniel Radcliffe, who also performed with Richard Griffiths in the stage play Equus at the age of 17, praised the actor’s “encouragement, tutelage and humor”.

Daniel Radcliff said: “Any room he walked into was made twice as funny and twice as clever just by his presence. I am proud to say I knew him.”

Fellow Withnail & I star Richard E. Grant said: “Chin-Chin my dear friend. I feel too gutted to talk without falling apart. Suffice to say I feel I’ve lost my adored Uncle Monty.”

Richard Griffiths’ family last night refused to comment on whether the University Hospital of Coventry and Warwickshire, renowned for its treatment of heart problems, were at fault.

Richard Griffiths died on Thursday at the age of 65 from complications following heart surgery .

Long-term friend Jane Harrison, 70, said: “Richard was wonderful but he was showing his age towards the end. No one knew just how poorly he really was.”

A spokesman for Coventry and Warwickshire Hospital said: “We are aware of this situation and we have been in touch with our executive. We cannot give out any further information due to patient confidentiality.”

[youtube 92mXB4m0QfA]