The Italian government has given the green light to a new high-speed rail line that would cut the train journey between London and Italy to just six hours.

The Turin-Lyon high-speed railway has been in limbo for months after the country’s new populist government threatened to cancel it.

But in a statement Italy’s prime minister Giuseppe Conte committed to completing the project, ruling that it would cost too much to scrap.

The line, which will run in tunnels under the Alps, cuts the journey from Milan to Paris and beyond by three hours. 

Existing TGV services between Paris and Turin currently take five and a half hours, with a journey time of seven hours to Milan. After the new line is complete the Paris-Milan journey will be cut to four hours.

A direct service through the channel tunnel from London would take around six hours to reach Italy.

But any company that decided to run such a service would have to wrestle with passport control and security regulations, which apply to trains between the UK and the continent.

With a completion date of 2030 for the new line, planning of any service is far off. Even if no direct service were introduced to the UK, passengers from London changing trains in Paris would be able to get to Italy three hours faster.

“Not building the high-speed line would cost much more than building it,” Italy’s prime minister Mr Conte said in his statement.

“The decision not to carry out the work would expose us to costs resulting from breaching our agreement with France.” 

Mr Conte said the EU had agreed to shoulder a larger proportion of the project’s cost – up from 40 per cent to 55 per cent of the €25bn (£22bn) bill. France’s national assembly has already approved the project.

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The project was the subject of a row between Italy’s populist coalition governing parties. It is supported by the League, which has traditionally been strong in the north of the country, but was opposed by the Five Star Movement, whose support base is mostly in the south.

The line is 270km long, of which 57.7km is tunnelled. It will connect with the LGV Sud Est high-speed line at the French end and the Turin-Milan high-speed railway at the Italian end. A service to London would use HS1 through Kent and LGV Nord through northern France, likely bypassing central Paris on the LGV Interconnexion Est line.

International rail services from the UK got a boost last month after Eurostar stepped up its new service from London to Amsterdam, adding an extra train per day. But last year German railway company DB ditched plans to run a direct service to Cologne and Frankfurt, citing operational difficulties. 

Unlike the vast majority of European countries the UK is not a member of the Schengen passportless area, which means international rail passengers must go through passport checks at stations. This makes it harder for firms to run international rail services, because they often require expensive modifications to existing stations to introduce border controls. Passengers in other EU countries benefit from seamless cross-border travel.