Cultural experts fear that Government plans to split English Heritage could put the future of the nation's heritage "in peril", while further concerns were raised that the move could prove a "stalking horse" for privatising cultural assets.
The National Trust has questioned whether the plan "stacks up", and asked whether the new bodies will still be able to protect at-risk sites, or if their ability to promote heritage will be damaged.
The Culture Secretary Maria Miller will tomorrow reveal details of the plan to overhaul English Heritage, and put it out for consultation. Ms Miller will say: "Our historic buildings are loved by everyone, and act as a magnet for tourists from all over the world. English Heritage sites like Stonehenge, Hadrian's Wall, Tintagel Castle and Battle Abbey are at the very heart of what England is all about. As such we want them to be able to give them the tools they need so as they can generate their own income."
In a radical proposal, the management of the 440 historical sites will be split into an independent charitable trust that will keep the name English Heritage.
The body aims to be self-funded by 2023, saying charitable status would allow it more freedom than state-run organisations to raise and invest capital and attract other funding, while benefitting from the tax breaks the status brings.
The rest of the operation, which deals with planning applications, offers expertise, and protects historic buildings by giving them listed status, will remain with the Government and is likely to take on the name "Historic England".
Simon Thurley, the chief executive of English Heritage, said: "This is the only way forward for us now. It's better for the nation's heritage and the people who visit our sites. This is also major news for the whole cultural sector."
Not everyone is as positive about the proposed change. Issues have been raised about the plan, including whether Historic England, the body remaining with the Government, might see its funding slashed or could even be abolished, leaving historical sites vulnerable in the future. Helen Goodman, the shadow culture minister, said: "There must be no watering down of English Heritage's role in planning. That is huge. If our building heritage is not defended as it should be that would be a terrible mistake."
Ingrid Samuel, the director of historic environment at the National Trust, said splitting English Heritage "raises some fundamental issues the Government needs to address through the consultation process".
These include the question of whether the new public body "responsible for protecting and promoting heritage [will] retain English Heritage's expertise and have the capacity to work with the wider heritage sector to fund and protect our historic fabric".
Richard Compton, the president of the Historic Houses Association, which represents historic houses in private and charitable ownership, said: "Our member houses depend on its expert advisory service and we would be extremely concerned if this were to be reduced or diluted in any way by the creation of a new charity to manage the state's property portfolio."
The "$64,000 question," according to one expert, is whether English Heritage in its new form will be able to remain the custodian of last resort to save heritage sites that are at risk or hugely unprofitable. Nigel Hewitson, head of planning at Norton Rose Fulbright and former legal director at English Heritage, said: "The distinction between English Heritage and the National Trust is that the former is the custodian of last resort. That's why a lot of their properties don't make money.
"The National Trust won't take properties on unless they have a dowry for future maintenance. Once English Heritage adopt that charitable status model they'll find it difficult to take on properties that are otherwise unviable."
Along with his management team, Dr Thurley has tabled a business plan to deal with the issue, which would involve the Government stepping in should any sites be threatened. He said: "We need to build this into the mechanism. Historic England has to be properly funded. If this arrangement damages our ability to be the custodian of last resort it will be a total catastrophe."
Only one other Government body, the Canal and River Trust, has changed to an independent charitable trust. "We're the first cultural body to do it," Dr Thurley said, "and I'm sure it will stimulate others to think in a similar direction."
To allow the monuments to be managed by a trust, the Government plans to give an £80m "golden handshake" payment in 2015 to allow the body to carry out major refurbishments across its sites. The conservation budget was frozen a decade ago which has left parts of the collection "in really, really poor condition". Dr Thurley pointed to sites including Netley Abbey in Hampshire, Castle Acre Priory in Norfolk and a "huge maintenance deficit on parts of Osborne House on the Isle of Wight. There are problems everywhere".
While the new English Heritage model aims to remove public spending, it is not strictly privatisation. The charitable trust is to manage, rather than own, the cultural sites, and the Government could revoke the licence and bring it back into state care.
Yet English Heritage believes the move reflects a wider ideology regarding the sector. Sir John Tusa, the former managing director of the Barbican, said: "The question is this: Is this the start of backdoor privatisation of major institutions? One could guess it's a stalking horse for more privatisation of culture; if it gets subsidies off the Governments books."
John Penrose, MP for Weston-super-Mare and former heritage minister, said: "I think it's a great idea. It will create stability for some of the country's most important heritage sites, and make English Heritage independent from political interference, and will create a cultural legacy which is every bit as important as the National Trust."