* Network to be completed by 2033, reach Birmingham 2026
* Extra tunnels to meet complaints of people living by route
By Tim Castle
LONDON, Jan 10 (Reuters) - Britain gave the green light on Tuesday for a 32.7 billion pound ($50 billion) high-speed rail network linking London, Birmingham and cities further north, delighting business groups but angering opponents along its route who say it is unneeded and will scar some of the country's prettiest countryside.
The first part of the route cuts through the Chilterns area to the northwest of the capital, a region of farms, woodlands and small towns, normally a heartland of support for Prime Minister David Cameron's ruling Conservatives.
"This is an immensely bad decision for Britain," said Martin Tett, chairman of an alliance of local councils fighting the scheme.
The line crosses the constituencies of several Conservative ministers and lawmakers in the area, who will be under pressure from local voters to rebel against the government when parliament finally considers the plans.
But the long-expected announcement was welcomed by trade unions seeking a boost to jobs at a time when unemployment is rising as the economy stagnates.
Government backing for the project was delayed from last December to give more time for Transport Secretary Justine Greening to consider ways of addressing the worries of opponents of the line.
To meet some of their concerns, extra parts of the route will be sunk into tunnels or cuttings.
Greening said she was confident the project would survive any legal challenges or judicial reviews sought by opponents.
"I think in parliament there is now a consensus in seeing this need to address capacity on our railway network," she said.
The Y-shaped network extending to Manchester in the north west and Leeds in the north will be built in two phases, with construction on the route from London to Birmingham starting in 2017 and the first trains running in 2026.
The full scheme would aim to be completed by 2033 and cost 32.7 billion pounds at current prices.
The project, known as High Speed 2 (HS2), would generate economic benefits of up to 47 billion pounds and fare revenues of up to 34 billion pounds over a 60-year period, Greening said.
The network would also have environmental benefits, she added, transferring to rail around 4.5 million journeys per year by people who might otherwise have travelled by air and 9 million from roads.
Constructing and operating the network would create jobs, with 40,000 jobs supported in areas served by the first phase of the network, which will include a direct link to Britain's existing high-speed line connecting London to France via the Channel Tunnel.
An extension to London's Heathrow Airport would be part of the later construction stage.
A parliamentary vote on the scheme is not likely until 2013 or 2014, but the government can be confident of winning any vote as the line is backed by the opposition Labour party, which first proposed the project before it was ousted from power last year.
Trains, initially running at 225 mph (360 kph) and later at 250 mph, will cut travel times between London and Manchester to an hour and eight minutes, a reduction of an hour.