Why are there sheep being herded across London Bridge?

You could be forgiven for thinking you'd not quite had enough sleep after spotting a herd of sheep being shepherded repeatedly across London Bridge.

But fear not. Today marks the annual Great Sheep Drive when Freemen of the City of London exercise their 'long-established right' to herd sheep over the capital's oldest river crossing.

More than 800 Freemen of the City took it in turns to herd two groups of 10 sheep back and forth over the bridge.

They were led by Barbara Windsor, 78, who was made a freeman five years ago.

Organisers hope to raise £40,000 for charity and throw the spotlight on the British lamb and wool industry.

The tradition dates back to the 12 century when traders were allowed to enter the city with the tools of their trade without paying a toll.

They were given the status of 'Freeman' meaning they worked for themselves and were not committed to working for someone else under the feudal system.

During the medieval period there would have been a number of guilds for everything from farming to baking, which a freeman could join.

The title of Freeman of the City, is largely now a ceremonial title but originally would have come with a number of perks including being able to wear a sword in public.

You can apply to join the Freeman of the City by being proposed by two existing members, paying a fee or as a reward for public service.

About 1,200 are created each year.