The problem arises when someone leaves a percentage of their estate to charity but executors are unable to trace and share out some of the assets. The Unclaimed Assets Charity Coalition says such assets can include forgotten bank accounts, land deeds, wage packets, company shares and the contents of safety deposit boxes.
The group, which is made up of eight charities, including Cancer Research UK, Barnardo's and Guide Dogs for the Blind, wants to pressure the Government and the banking industry to make it easier for executors to access old legacy assets. Under current rules, if an executor fails to find details of all the assets of an estate, all the beneficiaries due to receive a percentage will miss out.
Paul Farthing, legacy fundraising director at Cancer Research UK and spokesman for the group, said: "We want the Government to make information about unclaimed assets public. These days, people move around the country and to different jobs, so their assets are much more portable than before. There are lots of pockets where missing assets could be."
The coalition admits that its £1bn figure is based on estimates, but believes it is a conservative one. "We've made sensible estimates based on the facts we do know," said Farthing.
Calculations were based on figures provided by a range of organisations, including the Unclaimed Assets Register, an initiative run by an alliance of UK banks and building societies that helps people search for forgotten bank accounts.
The coalition has approached the Treasury and the British Bankers Association to discuss its demands. These include the adoption of a system similar to the online register of unclaimed assets in the US, www.unclaimed.org, which helps in the search for assets.
It also wants the Government to compel banks to surrender unclaimed assets and to reduce from 15 to five years the length of time banks can hold on to untouched accounts before defining them as dormant.
"In the US, this is seen as a consumer rights issue," said Farthing. "All that money is idle at the moment - but whose is it anyway? It could be out there, working for good causes."