Lawyers acting on behalf of Edinburgh City Council are preparing new legislation which would scrap rules preventing new buildings in Princes Street Gardens, the Meadows, Calton Hill, Bruntsfield Links and Leith Links.

Officials insist the move is required because the current law has delayed plans to replace the Ross Bandstand for several years.

But conservationists fear the changes will "open the floodgates" to development on the sites and pave the way for parts of the parks to be either sold off or built over.

One senior council source warned the new legislation could potentially allow any cash-strapped future administration to "free up bits and pieces of land in order to raise a bit of money to maintain them [the parks]".

Terry Levinthal, director of the Scottish Civic Trust, expressed alarm over the move. He pointed out that in the early 19th century, the citizens of Edinburgh had to take the town council to court to prevent Princes Street Gardens from being built on.

"Amenities like the Meadows and Princes Street Gardens are there in spite of the council, rather than because of it," he said. "You have to keep in mind that the council wanted to build a motorway on stilts through the Meadows in the 1960s.

"And in the 1950s, the council proposed building a bus station and multi-storey car park in East Princes Street Gardens.

"What has protected the Links, Princes Street Gardens and the Meadows has principally been the legal framework."

Mr Levinthal said that while there was nothing "inherently wrong" with replacing ageing structures in parks, he stressed any plan for a new multi-million-pound Ross Bandstand must not leave the world-famous gardens in the shadow of Edinburgh Castle "developed beyond recognition".

He added: "There are few other cities in the world that have such fantastic green spaces as Edinburgh. We would be very concerned with anything that could erode the assets of the city, including these green spaces."

The existing law, banning the building of significant structures in the parks without special parliamentary approval, was introduced by the old Edinburgh District Council in 1991.

It means that only "bandstands, public conveniences, police boxes and buildings for housing apparatus for the supply of electricity or gas" are permitted in the Meadows, Bruntsfield Links and Leith Links. The rules played in a role in the council's decision to scrap a controversial proposal for a skate-park in the Meadows.

The capital's outgoing Labour-run administration ordered the review of the legislation and has commissioned solicitors to draft new two private bills. One deals specifically with Princes Street Gardens, while the other is aimed at loosening restrictions on the other parks.

Council chiefs say that the current rules make it difficult even to add a new fence or a pathway in the parks – or replace the pavilion at the Meadows.

But Moira Tasker, director of the Cockburn Association civic trust, said: "Much-loved and used public, green spaces, such as the Meadows, Princes Street Gardens and Leith Links, have been under threat from development for decades.

"Their importance to Edinburgh citizens and the landscape setting of the capital cannot be underestimated. We would vigorously oppose any attempt to remove the legislation protecting these green 'lungs' for future generations to enjoy."

Bob Cairns, who was planning convener on the former Edinburgh District Council when private legislation was put into effect in 1991, said it had been intended as "symbolic gesture".

He said: "It was done with good intentions, but with hindsight the legislation was too restrictive."