British museums have joined forces to ask the government for an extra £115m a year at what they say is a "critical time" for their services.
Museums are vital to education and tourism, the manifesto says
A Manifesto for Museums, launched on Tuesday, contained a warning that large London attractions may not be able to keep going at their present levels.
An extra £50m a year is needed to keep current services running, it said.
Another £15m is also needed for work with regional museums - which require an extra £35m on their own, it said.
A further £15m per year is required to buy new objects, it added.
"This is a critical time for our museums and galleries," it said.
UK MUSEUMS AND GALLERIES
The UK's 2,500 museums and galleries receive 100 million visits per year
Four out of the UK's top five tourist attractions are museums
37% of UK adults and 50% of school-age children visit museums and galleries at least once a year
85% of overseas visitors say museums and galleries are among the main reasons for coming to the UK
The museum sector is worth £3bn to the UK economy
Source: A Manifesto for Museums
The government released figures on Tuesday which it said showed the policy of universal free admission for England's national
museums and galleries was a huge success.
It said the policy had attracted almost 11
million extra visitors in its first two years, with visits up by 72% at the former charging museums.
Arts minister Estelle Morris said: "This is excellent news. Government investment to help scrap admission charges has paid a rich dividend, with 13.3 million people visiting the former charging museums last year, compared to 7.7 million when the turnstiles were in place."
The five-year manifesto cited research saying the attractions were vital to education, tourism, research and the economy.
More than 100 million people visit the UK's 2,500 museums and galleries every year, it said.
And 85% of overseas visitors say the establishments are among the main reasons for coming to the UK.
Without more money, the abilities of national museums to carry out their statutory obligations and sustain existing contributions to government agendas was "put at risk", it warned.
The museums also need the extra £50m a year to extend access to their artefacts, modernise and build up collections and update conservation facilities.
There is also a backlog of £150m of building repairs waiting to be done, it said.
For local museums, the extra £35m would be used to extend the Renaissance in the Regions scheme that has already improved collections and boosted visits in the north east, south west and West Midlands.
The manifesto calls for another £15m for collaborations between national and regional institutions, plus £15m to buy new objects.
"This will only go some way to beginning to address the problem but is vital if our institutions are to maintain their pre-eminence and relevance," the manifesto said.
"We need to be able to collect in the present and not simply preserve the past. Such collections are an essential part of our legacy to the future."
The manifesto was drawn up by bodies representing a range of museums - from the biggest London attractions to local establishments.
Tate director Sir Nicholas Serota told BBC Radio 4's Today programme that central government and local authorities may not appreciate the "gems" they had.
"Museums are like libraries and schools - part of the fabric of society which should be provided in a way that makes them accessible to all," he said.
Tuesday is due to begin with a press conference to explain the sector's needs at the National Gallery in London.
Later in the day, there will be a debate at the Tate Britain and a parliamentary reception hosted by the Museums, Libraries and Archives Council (MLA).
The Department for Culture, Media and Sport (DCMS) will decide on any funding change after Chancellor Gordon Brown's comprehensive spending review in June.
A DCMS spokesman said: "Through the summer, we will cut that cake between museums, the performing arts, heritage, sport, the various tourism boards and the other mouths we have to feed.
"Of course, we are entirely convinced of the importance of museums both in the educational and creative terms."
But it would ultimately be down to the Treasury to decide whether museums would get the extra £115m.
The groups that have signed up to the manifesto are:
The Directors of the National Museums
The Museums, Archives and Libraries Council
The Association of Independent Museums
The Group for Large Local Authority Museums
The Museums Association
The Regional Agencies