Heathrow may have to build 'green bridges' and underpasses for wildlife as part of its £33 billion third runway expansion, new Government blueprints reveal.

The proposed measures are included in ministers' draft plans for the long-awaited development, which will see a new 3,500 metre (2.1 mile) runway installed at Britain's busiest airport.

Under the plans, the preferred developer Heathrow Airport Limited (HAL) will have to protect the local environment and stop the huge infrastructure project carving up wildlife habitats.

Transport Secretary Heidi Alexander hailed the new Heathrow Expansion National Policy Statement as an 'important milestone' and 'critical to national growth'. 

However, the document says the development must be 'designed and landscaped to provide green corridors and minimise habitat fragmentation', adding this could include 'underpasses or green bridges to link habitats'.

The requirement raises the prospect of wildlife crossings being built as part of the mega-project, in an echo of the controversial £125 million HS2 tunnel constructed to protect rare bats from passing trains.

Heathrow Airport currently manages 13 biodiversity sites across 170 hectares, making up about 10 per cent of its total footprint. These include reedbeds, grasslands and woodlands, supporting more than 3,000 species.

The runway development is expected to cost £33 billion, including £1.5bn to move the M25 motorway, and is expected to be financed privately.

The proposal is likely to fuel concerns that flagship infrastructure projects are being loaded with costly environmental mitigation measures before they can get through the planning system.

The draft plan says developers must 'take advantage of opportunities to conserve and enhance biodiversity' and time construction work to avoid sensitive periods, such as wild bird breeding seasons and the life cycles of migratory fish.

The expansion must be compatible with climate targets, not breach air quality limits and ensure noise emissions are not worse than 2024 levels, with reductions where possible.

The developers will be required to offer noise insulation to local homes and public buildings, such as schools, and provide a public compensation fund worth £750 million to be distributed to local communities over 15 years.

Campaigners have long warned that the project will mean more noise, pollution, traffic and environmental harm for communities around west London.

However, Chancellor Rachel Reeves has said she is determined to get 'spades in the ground' for the third runway and for it to be built by 2035.

Launching a public consultation on the new Heathrow policy statement on Thursday, Ms Alexander said it was 'an important milestone and step forward'.

'The Government considers that the development is critical to national growth,' she said. 'This is a signal of the importance the Government places on the need for expansion and will be an important additional factor in the planning balance.'

Heathrow chief executive Thomas Woldbye said he 'strongly welcomed' the new blueprints.

'The UK cannot realise its full economic potential without an expanded Heathrow and this is an important step towards delivering the capacity the country needs,' he said.

'We will now focus on securing planning permission and delivering this vital project.'

Alethea Warrington, head of aviation at climate charity Possible, said the Government was 'living in a fantasy land if it thinks it can allow a new runway without making noise pollution even worse, making our air even more toxic, or crashing through our climate targets'.