Culture ministers are at odds with their Treasury counterparts over plans which could mean museums losing thousands of pounds in tax relief.
The Natural History Museum is in Michael Portillo's constituency
Arts Minister Estelle Morris told MPs in Westminster Hall talks were still continuing over the Treasury's plan to close a loophole which allows museums to claim gift aid by asking for donations in lieu of admission charges.
She told MPs: "I am campaigning about gift aid. It is not my sole comradely difference of opinion with the Treasury."
The debate was opened by Michael Portillo, whose Kensington and Chelsea constituency includes the Natural History and Science Museums, and the Victoria and Albert Museum.
Next week the National Museum Directors' Conference will publish reports highlighting the social, education and economic importance of museums, as well as their role as sources of creativity.
Museums 'losing out'
Mr Portillo said museums were losing out in the distribution of funds from the Department of Culture, Media and Sport in comparison with the arts and sport.
Between 2001-02 and 2005-06, he told MPs, sport will receive a funding increase of 91% and the arts 63%, while museums, galleries and libraries get 26%.
Traditional displays of artefacts are just one aspect of museums' work
In a debate which saw few disagreements between the parties, the Labour MP and former Culture Secretary Chris Smith said in the coming spending round, "museums should be given priority".
Mr Smith was one of several MPs to raise the issue of gift aid.
The Conservative MP Robert Key warned that the withdrawal of the concession would have a "dire impact" on his local museum, the Salisbury and South Wiltshire.
For the Liberal Democrats, Don Foster pointed to differences between the Treasury and Inland Revenue over gift aid: "The Treasury claims that the scheme is a loophole, even though in 2000 the Inland Revenue produced a note that specifically informed museums and art galleries of the opportunity it offered."
Local council cuts
Both Mr Key and Mr Foster highlighted the impact on museums of cuts in local authority funding.
Don Foster told MPs that because of funding difficulties Somerset County Council is now discussing the reintroduction of entrance fees at its major museums.
Replying to the debate, Arts Minister Estelle Morris acknowledged the importance of museums in society.
She said the present Government had to deal with museums which under the previous administration had faced a 17% real terms cut in funding between 1993 and 1997.
But she accepted that museums recently have not had the "lion's share" of DCMS funding, and said she hoped the power of the argument for increased resources would be heard in the corridors of the Treasury.
You can see the full debate on BBC Parliament at 0600 on Saturday 6 March.