Cameron's wife uses photograph of Tory leader and disabled son to sell Christmas cards

The picture, which shows the Tory leader gazing into the eyes of his eldest child, Ivan, is displayed on the website of Smythson, the Queen’s stationer.

The 120-year-old company, which has its flagship store in Central London and branches worldwide, last night attempted to play down the use of the image, describing it as an unfortunate oversight.

Touching: The advert using David Cameron and Ivan as a baby appeared on Smythson's website

A spokeswoman said there had been ‘no intention’ to use the Cameron family to promote Smythson, and the picture would be removed from the website.

Mr Cameron’s office added that Samantha, who has been Smythson’s creative director for 11 years, was ‘mortified’ but the episode will also embarrass the Tory leader, who has faced accusations in the past of exploiting his family for political gain.

Stephen Pound, the Labour MP for Ealing North, said: ‘I would have thought that if there was one thing that MPs have learned over the years, it is that if they use their children it will come back to haunt them.’

At home: Cameron at home with his son, who has cerebral palsy, in March

The picture of Mr Cameron and Ivan, who suffers from cerebral palsy, was used to demonstrate Christmas cards that customers can personalise with their own photographs.

The set of cards, which feature holly borders and come with hand-lined envelopes, are part of Smythson’s 2008 range and cost from £409 for 100.

A spokeswoman for the company, whose customers include model Claudia Schiffer, artist Damien Hirst and fashion designer Tom Ford, said no one had noticed the identity of the picture’s subject because Mr Cameron’s face was partly obscured by shadow.

She said directors had donated pictures of their children to be used on the company’s website and that it was one of three provided by Mrs Cameron in 2004, a year before her husband became Tory leader.

The spokeswoman said they accepted that use of the photograph was ‘inappropriate’, adding: ‘It is a totally different situation now from when it was first provided for use. At the time it wasn’t an issue.’

A Conservative Party spokesman said: ‘David wasn’t aware that these photos had been used but appreciates this was a genuine error.

‘Sam had forgotten all about them and is mortified. This is a mistake and not in any way an attempt to use Cameron family pictures to promote Smythson.’

Mr Cameron told The Mail on Sunday, in an interview last year, that his wife tries to avoid capitalising on his position to publicise her company, which was granted the first of its four Royal warrants in 1964.

Mortified: Cameron and his wife Samantha on holiday this year