The Scottish Government's wildlife watchdog ignored the advice of its own experts and bowed to political pressure to allow a nature conservation area to be damaged by opencast coal mining.

A raft of internal emails released under

Freedom of Information laws reveal that Scottish Natural Heritage (SNH) was repeatedly told by its staff not to allow the expansion of the Grievehill mine in East Ayrshire because of the dangers it posed to golden plovers, short-eared owls and hen harriers.

But, after being lobbied by politicians and threatened with legal action by the developers, SNH withdrew its objection and gave the expansion the green light in 2007. The following year, there was a "bog burst" at the mine, which ended up with the mining firm, ATH Resources, being fined £10,000 in 2010 for damaging a wildlife area.

Last year, the company went bust, leaving Grievehill derelict and with no money to restore the landscape as had been promised.

Aedán Smith, head of planning and development at RSPB Scotland, said: "It was always clear that SNH staff shared our concerns about the environmental damage that would be caused by mining this important wildlife site. It was therefore extremely surprising when they pulled the rug from under us and Scotland's wildlife by dropping their objection."

Work was started at the opencast coal mine near New Cumnock in 2005, and ATH Resources applied to extend the site in 2006. SNH objected to the extension in 2007 because it would damage the Muirkirk peatlands, protected by two conservation designations.

The released emails show that, in 2006 and 2007, SNH staff were strongly in favour of objecting. But in August and September 2007, SNH received letters from two local Labour politicians, Sandra Osborne MP and Cathy Jamieson MSP, urging that the extension be given the go-ahead to preserve jobs.

And lawyers acting for the developer threatened legal action if SNH blocked the extension. SNH later withdrew its objection, allowing the extension to go ahead.

Roddy Fairley, a senior manager at SNH, said that it was not uncommon for SNH to be lobbied by politicians and lawyers about controversial developments.

SNH withdrew its objection only after an unusual and legally binding mitigation plan had been agreed, he said. "There was not any persuasive view that the mitigation eventually proposed was less than adequate."

"If others are worried that this approach represents SNH 'rolling over' in the face of demands from developers, my feeling is that it shows the opposite. Not only did we require a legally binding commitment from the developer, but we also drove the issue into the courts when it went wrong."

Greta Roberts from the Mining and Environment Group Ayrshire (MEGA) criticised SNH for "watering down" its objection. "SNH has good professional staff at local level, but HQ is too close to the Scottish Government and is clearly not acting as guardians of our environment."