A daily 7.5g bar of the chocolate can change the underlying skin stucture of a 50 year old to that of someone in their 30s, say developers.

It may seem too good to be true, but guilt-free chocolate which promises to slow down the emergence of wrinkles and sagging skin, has been developed by scientists.

"Esthechoc" the brainchild of a Cambridge University spin-off lab, claims to boost antioxidant levels and increase circulation to prevent lines and keep skin looking youthful and smooth.

Just a small 7.5g bar of anti-ageing chocolate contains the same amount of the antioxidant astaxanthin as a fillet of Alaskan salmon, and equal levels of free-radical fighting cocoa polyphenols as 100g of dark chocolate.

Its makers say it can change the underlying skin of a 50-60 year old into that of someone in their 20s or 30s. Tests showed that after four weeks of eating the anti-ageing chocolate every day, volunteers had less evidence of inflammation in their blood and increased blood supply to skin tissue.

Creator Dr Ivan Petyaev, a former researcher at Cambridge University, and founder of biotech firm Lycotec, said: "We're using the same antioxidant that keeps goldfish gold and flamingos pink.

"In clinical trials we saw that inflammation in the skin starting to go down and the tissues began to benefit.

"We used people in their 50s and 60s and in terms of skin biomarkers we found it had brought skin back to the levels of a 20 or 30 year old. So we've improved the skin's physiology.

"People using it claimed that their skin was better and we can see that the product is working to slow down ageing."

As the bar contains just 38kcal its makers say it is even safe for diabetics.

But 'Esthechoc' is unlikely to be available in Britain's corner shops. The confectionary, which is also called 'Cambridge Beauty Chocolate' comes boxed as a three week supply, individually wrapped, and will only be available in high end retailers from next month.

It is also likely to come with a hefty price tag, although its makers were unwilling to reveal the cost before its official launch at the Global Food Innovation Summit in London next month.

According to its brochure the target market are "elegant, educated and affluent' city-dwelling women in their 30s, and businessmen 'to support their appearance in a stressful environment and on their business travels".

However health experts were cautious about the product,

Naveed Sattar, Professor of Metabolic Medicine at Glasgow University, said more robust clinical trials would be needed to validate the 'ridiculously strong' claims made by the company.

"There may be biological reasons to think some of the compounds may benefit some processes linked to ageing and disease but on the other hand, eating too much chocolate means more calories, which means obesity so the net effect is never clear cut.

"These food claims need to be back up with trials to have any genuine credibility. Such trials are glaring by their absence so all such health claims are unfounded."

Nutrition experts at University College London also warned that previous trials showed that astaxanthin worked better when applied directly to the face rather than ingested.

UCL nutritionist Dr George Grimble said: "There is a potentially sound scientific base to this although it is obviously early days.

"There needs to be further clinical trials to show that it is safe but astaxanthin has been shown to have antioxidant effects and low toxicity, so from that respect, it seems promising.

"Using dark chocolate is quite clever. As a nutritionist, I am generally in favour of dark chocolate.

"So it's got a good track record in terms of the science but it is too early to say what the long term benefits might be.

"In my humble opinion, it would be necessary for the company's in-house trial to be submitted for publication in a peer-reviewed journal in order for their health claims to be substantiated."