Future generations will be grateful if HS2 is built, the boss of the controversial project has claimed.
HS2 Ltd chief executive Mark Thurston said the UK must hold its nerve over the high-speed railway scheme, amid growing concern about finances and the environmental impact.
A report by the House of Lords Economic Affairs Committee last week warned it was "far from convinced" HS2 will be built within its #55.7 billion budget.
The committee said the cost of the project could be cut by reducing the speed of the trains and moving the London terminus.
Former HS2 chairman Sir Terry Morgan has claimed the railway cannot be built to its current specification on budget.
Phase one is due to open between London and Birmingham in December 2026, before the railway is extended to Crewe, Manchester and Leeds.
HS2 trains will also serve locations on the existing mainline network, such as Liverpool, Newcastle, Edinburgh and Glasgow.
Mr Thurston said big projects such as the M25 motorway and the Channel Tunnel "divide opinion" in the early stages.
He told BBC Breakfast: "If you look back over history, we've held our nerve on those big projects.
"It's unthinkable that you would travel to France from London now without getting the train.
"So I think we need to see the ultimate prize, the ultimate regenerative effect that HS2 is going to have on our economy. That's what I'm focused on.
"As much as it takes a long time, as much as it takes a lot of public money, future generations will thank us for completing this programme."
HS2 Ltd announced on Thursday that work to build the railway is supporting 9,000 jobs around the country, with activity on more than 250 sites.