The tree, in a suburban street in Weybridge, has been assessed according to its size, health, historic significance and the pleasure it brings to residents.

	The oak tree in Weybridge, Surrey that has been valued at £500,000

It has been valued under a new system adopted by several councils to stop healthy trees from being cut down because they have been blamed for subsidence in buildings.

Capital asset value for amenity trees (Cavat) means that from now on, risk-adverse councils or insurers will have to undertake extra engineering work to prove a link between a tree and subsidence, which can also be caused by broken drains and dry weather.

It is hoped it will stem the tide of older, healthy trees that are felled each year by insurers and councils on spurious grounds.

In London alone, more than 16,000 trees including some over 100 years old have been chopped down because of insurance claims in the past five years, although the London Assembly said that only one per cent of those removals were justified.

The Weybridge oak, which is around 40 feet high with branches stretching around the same width, is thought to be over 300 years old, although an exact age cannot be established without damaging it be taking a tissue sample for carbon dating from the centre of its trunk. English oaks can live for up to 600 years.

Its value has been calculated using a complicated mathematical equation that sees Pi multiplied by the radius of the tree at its based squared.

This sum is then assessed against nursery rates for planting and producing a similar tree, with value added or subtracted depending on the tree's location and local residents' level of attachment to it.

David Munro, from Surrey County Council, said that in reality, the tree's monetary value was simply a tool to determine the level of protection it should receive.

"The real value is its history and contribution to the environment and the amount of pleasure it gives our residents, which is considerable," he said.

The country's most expensive tree is currently a plane tree in Berkeley Square, Mayfair valued at £750,000.

In London alone, the value of trees is estimated at £6.4 billion under the new system, with traditional English trees such as oaks, horse chestnuts, planes and beeches emerging as the most valuable.