“Dear Gordon Brown, I can save you £508m a year.”

These are the words a Hampton mum has plastered across UK billboards, inviting the Prime Minister to call her to find out how “when it’s convenient”.

In a bid to raise awareness about autism, Polly Tommey also went to 10 Downing Street with her autistic son Billy to deliver a letter requesting a personal meeting with Gordon Brown.

Mrs Tommey, who founded the Autism Trust, believes if more help was given to help autistic people find work – and relatives forced into acting as full time carers – the Government would see a vast reduction in the benefits they pay out.

Currently, six per cent of adults with the condition are in full-time employment and Mrs Tommey estimates if that number reached 25 per cent, savings would be in excess of £500m.

“Imagine what we could do if we could help 30 or 40 per cent,” she said.

“We want better support, politicians to engage with us and the acknowledgement and support our children deserve as fully contributing members of society.

“Unless the problems of autism are understood, and services and support become more available, we will see an underclass of disaffected and desperate autism households emerge.”

The £500,000 billboard campaign has been funded by commercial donors to allow Mrs Tommey to make her personal appeal in a very public way.

The mum of three accused the Government of ignoring the “overwhelming stress and demands faced by families of those with autism”, despite over 500,000 people in the UK having the condition.

She added: “Billy has a bleak future today in our blinkered world.

“He is an inspiration to all of us in our family and everyone who meets him.

“It is simply not fair that his potential is dismissed.”

For more information visit theautismtrust.org.uk.