This documentary investigates the history of lunch, a meal that we now eat in a speedy average of 12.49 minutes. But 300 years ago lunch didn't exist at all - for centuries our daytime meal was called, as it still is in some parts of the country, dinner, a long-standing confusion that Clarissa attempts to unravel.

Lunch is the workhorse meal of the day and the story of its origins and evolution is really a history of our working lives across the centuries. Medieval farm labourers used to sit down to eat as early as 10am, but they had been toiling in the fields since daybreak. As she tucks into some of the dishes of the day, Clarissa explodes some common myths about our ancestors and their eating habits. Not all their fish was salted and people didn't eat rotten meat flavoured with spices, but they certainly did eat vegetables - and, back then, carrots were purple.

Moving forward through history, Clarissa tries a 17th-century recipe for venison that was a favourite of the diarist Samuel Pepys and discovers that the long business lunch of the 1980s already existed in the 1660s. By Victorian times, office workers were sitting down to steaming hot plates of mutton chops and oxtail stew in a chophouse, and Clarissa calls in to one of the last surviving examples in the City of London.

However, it is the Earl of Sandwich's famous convenience food invention from the 1750s that has come to dominate our modern lunchtime menu. All the same, the ubiquitous sandwich can still be an opportunity for creativity and inventiveness, and as she comes towards the end of her journey through history, Clarissa meets Britain's most celebrated sandwich designer and samples his most stunning original creation, which has been officially declared to be the world's greatest sandwich.