Dishes of chicken blancmange and porpoise porridge are unlikely to whet the appetite of most modern food lovers.

But such recipes were apparently fit for a king 600 years ago.

Written by chefs employed by Richard II, they are included in what is thought to be the world's oldest cookbook.

The unusual dishes rival modern creations by British TV chef Heston Blumenthal, who is famous for his snail porridge.

Experts from Manchester University's John Rylands Library, who discovered the manuscript, have translated a handful of its 150 recipes, which are written in Middle English and date back to 1390.

They include frumenty, a porridge-type dish made of bulghar wheat, chicken stock and saffron, and payn puff, a dish of boiled fruits wrapped in pastry.

The unusual cookbook, called the Forme of Cury, is believed to have contained dishes to feed servants and the royal family alike.

It gives a fascinating insight into the delicacies of the time, including dishes of swan and peacock. After translating the recipes, historians wanted to try the dishes themselves.

However, with no ingredient quantities or instructions, making the dishes proved tricky. John Hodgson, who looks after the library's manuscripts and archives, said: 'One of the difficulties was that a lot of the recipes were very vague.

'It wasn't like Delia Smith or Gordon Ramsay books at all. The book doesn't specify quantities of ingredients or cooking times, so it was a case of trial and error to get the recipes to suit modern tastes.'