Hollywood star Robert Downey Jnr  – known to millions as Iron Man – has donated a once-in-a-life-time auction prize to raise funds for Julia’s House, the Wiltshire and Dorset children’s hospices.

The actor has offered one lucky winner the chance to join him on the red carpet at the world premiere of his new film - Marvel’s Avengers: Age of Ultron - along with a string of other goodies, including a helicopter flight over Los Angeles.

The funds raised will be a welcome boost to Julia’s House which wants to offer more families access to its support and has just announced plans to build a hospice in Wiltshire.

Entries can be made through Omaze, an American organisation that supports charities and provides opportunities for anyone to pay $10 (£6.50) and enter a draw for unique celebrity experiences. There is no limit on the number of entries per person and the winner is selected randomly by computer.

Robert Downey Jnr became interested in Julia’s House after he attended a fundraising event at the home of film director and Julia’s House patron, Guy Ritchie.

Martin Edwards, CEO of Julia’s House, said: “We are so grateful to Robert Downey Junior for helping with our dream to increase our respite and end of life care and reach more children over a wider geographical area, principally by building a Wiltshire children’s hospice and extending our home care in the county.

“It’s amazing when someone in so much demand is so focused on giving something back. He’s our superhero - we love you Iron Man!”

Julia's House, which already offers home-based community care in South Wiltshire, wants to extend its support to other families with life-limited children by building them a small, dedicated hospice from which it can provide a county-wide care service.

To do this it has launched a public appeal to raise £1.5 million towards the £3m total.

To buy tickets fpr the Robert Downey Jnr draw visit Omaze.com and for information about Julia's House visit juliashouse.org