For six centuries it bridged the Thames and was a unique feature of the capital.

Old London bridge, immortalised by nursery rhyme, was the longest inhabited bridge in Europe, with homes built above dozens of shops along its 905ft span.

And despite being demolished 170 years ago, the bridge continues to have an influence on the lives of millions.

A new history of the bridge, published yesterday, tells how it bequeathed a legacy to London; a little-known charity which now has multi-million pound assets.

The Bridge House Estates, a registered charity, can trace its history back to 1097 when William Rufus, son of William the Conqueror, raised a special tax to repair the wooden London bridge.

When the stone bridge was completed in 1209, it raised taxes, rents and bequests "from a widow's gold wedding ring, worn thin, to numerous valuable revenue-producing properties given 'to God and the bridge', according to Patricia Pierce's book Old London Bridge.

The charity went on to build Blackfriars bridge, purchase Southwark bridge and, just over a century ago, construct Tower bridge.

Its most grotesque role was collecting rent for the spikes on Old London bridge, used to hang the heads of traitors executed at the Tower.

Its funds were skilfully administered and the charity now has assets, divided between gilts, bonds and a portfolio of commercial properties, of more than £600m.

Bridge House Estates has sole responsibility for the four City bridges. If one collapsed, the fund would be required to rebuild it from its own resources without the help of the taxpayer.

Since 1995, the charity has widened its remit to donate millions of pounds in surplus funds to other good causes, including transport and access for the elderly and disabled and a £4.5m grant to the infamously wobbly millennium bridge.

The author said: "Nobody knows this, that I've ever met, apart from people involved in the Corporation of London [the trustee of the charity].

"Bridge House Estates received so much money from old London bridge - the tolls, the rents, property left to the bridge. This was accumulated over hundreds of years, and it has been invested by those men in the city who know how."

Until 1750 this was the only bridge in London over the river Thames, and from its completion it was famed throughout Europe.

While there were other habitable bridges in Europe - 35 in France alone - this was the longest, and took 33 years to construct.

Its nineteen weir-like piers created fearsome rapids where thousands drowned, some thrill-seekers even 'shooting the bridge' in a medieval version of white water rafting.

The author also notes that the execution of Scottish hero William Wallace launched "a gruesome tradition forever linked with the bridge" when his head was placed on the Drawbridge Gate in 1305.

"It was impaled on the gate in the sight of both land and water travellers to become a kind of fourteenth century tourist attraction, the citizens having been told that Wallace was exceptionally evil."

The sight of severed heads on the bridge was never forgotten either by the citizens or by foreigners approaching London, she writes. Visitors recorded seeing as many as thirty-four heads at one time.

Old London Bridge, by Patricia Pierce, is published by Hodder Headline, price £14.99.