The warning came as the British Museum revealed it is being asked to choose between a pounds 5 entry fee or the loss of 350 jobs.
The museum's government grant for day to day running was cut by 3 per cent this financial year. The museum will also cease to receive annual contributions from the British Library for its share of the running costs of the building after it leaves for its new home in St Pancras, central London, in 1998.
It has reviewed its operations, producing a report which concluded the greatest outgoing lay in the salary bill while the income of the museum could best be increased by introducing admission charges.
By the end of the decade, the museum's shortfall in funding, compared with the 1996 position, could be as great as 20 per cent. The Government has given no indication that it plans to give any additional grant to meet this deficit or the costs needed to rehabilitate library space transferred for museum use.
According to staff at the museum, the only alternative to 20 per cent job cuts and a pounds 5-pounds 6 admission charge would be reduced opening hours, increased gallery closures and shedding one-third of the staff. They described the coming changes as a tragedy in the making and protested that attempts by other museums to introduce charges have done little to improve their parlous finances, instead encouraging the treasury to make further cuts in grant.
The Victoria and Albert Museum, in London, which has seen admissions fall since the introduction of "voluntary" admission fees 12 years ago, recently announced that a pounds 5 charge will become compulsory.
The Museums and Galleries Commission chairman, James Joll, said in its annual report, published today: "Increasingly museums are being forced to make operational decisions driven by financial pressures alone. In some cases this is forcing them to abandon the tradition of free access for all.
"As Budget Day approaches, central Government must recognise that further reductions in funding threaten the ability of museums to discharge their core responsibilities."
Museums have received millions in Lottery funds for capital projects such as building.
But the MGC director, Timothy Mason, said in the report: "The capital plenty of lottery funding is in stark contrast to the revenue impoverishment which gnaws at the financial heart of the day-to-day operation of many museums."
The MGC is the Government's adviser on museum matters and was put forward for a more pivotal role in the Treasures In Trust report unveiled by National Heritage Secretary, Virginia Bottomley, this summer.Reuse content