It is an ancient slimming remedy with a royal seal of approval.

Now a traditional herb used by King Charles II to help his mistresses lose weight could be used in the modern day battle against obesity.

Heath Pea
Heath pea: Could curb hunger pangs

Experts want to re-establish the humble heath pea to fight the nation's weight crisis after evidence of its use was discovered during an archaeological dig.

Heath pea, which is also known as bitter vetch, was used in medieval times as a hunger suppressant when the crops failed.

It was also passed around the court of King Charles, who gave it to his lovers who had a propensity for plumpness.

Monks used the plant to treat patients in the 14th century Soutra Aisle monastery near Edinburgh, which is currently being excavated.

Dr Brian Moffat, an expert on medieval remedies, said the idea to promote heath pea as a slimming aid had been developed after he came across the remedy during the dig at the Soutra site.

Dr Moffat, who is director of the dig, said it appeared the monks cut up the tubers of the plant to make a potion.

He said the tubers - which have a "leathery liquorice" taste - had the effect of making people forget to eat.

Speaking on a BBC Radio Scotland documentary to be broadcast next month, he said: "We have been dealing with some anonymous little tubers, which have been chopped up in to quarters.

"The tubers are of heath pea or bitter vetch.

"If you ate one of these pea sized tubers you are meant to 'not eat, not want to eat and not miss eating for weeks and even in to months'.

"They were actually used as a measure to ward off hunger once crops had failed in the fields.

"We thought we must take this further because the plants seemed to become obsolete really at the time when mass potato cultivation came in.

"Before that it was a common measure in crisis.

"We thought if this can ward off hunger for weeks in to months, and by all accounts they are otherwise innocuous, there are possibilities in this.

"We have taken our idea forward and set up a company, just upon the unlikely assumption that a medieval medicine might have modern usefulness."

He said the commercial possibility these days would be as a modern slimming pill for people wanting to lose weight, or for humanitarian purposes.

Sir Robert Sibbald, joint founder of the College of Physicians in Edinburgh and joint founder of the Botanic Gardens, held the plant in higher esteem than any other.

He grew it in his therapeutic herbal collection in 1670.

Dr Moffat added: "We know all about Heath Pea on the authority of Sir Robert Sibbald.

"He was a mainstream medical figure who actually set out to promote the heath pea, and in his writings he quite simply gives it more attention than anything else in Scotland - animal, vegetable or mineral.

"Sibbald esteemed it high enough that in his letters to his colleagues he called it Herba Scotica Miraculosa - the miraculous Scottish herb.

"It is a plant which is commonly usually overlooked today. It deserves a second look."

Richard Swift, head of the project, said: "The tubers could help boxers and other athletes train down to a weight as well as helping dieters exercise and lose weight.

"There could be a good long term market for the tubers."

Heath Pea (Lathyrus linifolius) is normally found in poor grazing and heath land. It sometimes grows alone, but it can also grow in clumps on banks and verges of roads and tracks.

The plants take two or three years to mature but require very little looking after.