The Conservative party will today seek to reinvigorate its environmental agenda with a high-profile pledge to ditch plans for a third runway at Heathrow in favour of a TGV-style high-speed rail network linking London, Birmingham, Manchester and Leeds.

The party said that the 180mph line would aim to cut 66,000 flights a year from Heathrow by tempting domestic travellers onto trains capable of travelling from London to Birmingham in 45 minutes; London to Manchester in 80 minutes; and London to Leeds in 97 minutes.

The new line would also run out of Kings Cross St Pancras, creating a high-speed rail hub where travellers could transfer to Eurostar services to the continent.

The move was welcomed by environmentalists, who have recently criticised Conservative leader David Cameron for apparently distancing himself from previous commitments to develop a greener policy framework.

Shadow transport secretary Theresa Villiers said the high-speed rail proposals were driven by a desire to cut carbon emissions. "This is a seriously green decision," she told The Guardian newspaper. "A few years ago it would have been inconceivable for the leader of the Conservative party to say no to a third runway and putting the brakes on Heathrow expansion."

She added that a Tory government would invest £15.6bn from 2015 to 2027 in the new line with the private sector investing a further £4.4bn.

The proposals were welcomed by rail operator Network Rail, which earlier this year announced it is to assess the feasibility of building five new routes to the north and west of London.

"[These proposals] are not too far from what we are looking at," said a spokeswoman for the company. "There is already a big programme of rail expansion going on, and any further investment would certainly be welcomed by us."

She added that any new high-speed line would also deliver numerous knock-on benefits for the rest of the network by freeing up space on existing lines for shorter commuter journeys.

The proposals were also welcomed by Greenpeace Executive Director John Sauven, who said the pledge would put "real pressure" on Gordon Brown to rethink his stance on Heathrow expansion.

In a clear dig at the government's support for both airport expansion and new coal-fired power stations, Sauven said that "the Conservatives have recognised that decisions taken now on high carbon projects… will make or break our chances of tackling climate change in the future".

However, airport operator BAA accused the Conservative proposals of putting "Britain's future competitiveness at risk", arguing that a high-speed rail link would not solve the problems presented by a shortage of airport capacity.

"BAA believes this country needs both a third runway at Heathrow and high-speed rail," said a spokeswoman for the company. "To prioritise one over the other is a false choice."

She added that even if every flight from Manchester and Leeds/Bradford were replaced by a new high-speed rail line, Heathrow would still be operating at 97 per cent of capacity.