Rail passengers travelling from Scotland to London will see an average of half an hour shaved off their journey time from today after the completion of a £9bn upgrade to the west coast main line.

The decade-long works, one of Europe's biggest civil engineering projects in recent times, have reduced the average journey time from Glasgow Central to London Euston to four hours and 26 minutes from five hours.

This new journey time represents a 90-minute improvement on some services and an hour's less travelling time when compared to 2003, when the trip took five hours and 35 minutes.

Network Rail, which has overseen the works, promised a "quantum leap" in services following the completion of the upgrade yesterday. The frequency of trains will also be improved, with an hourly service operating for most of the day between London Euston and Glasgow Central for the first time.

Tom Harris, the Glasgow South MP and former transport minister, predicted the improvements would persuade more people away from short-haul flights and on to trains.

"I'm relieved the works are over and I think Network Rail have done a fantastic job," he said.

"I'll be getting the train myself tomorrow morning. It will make a big difference for people like myself who have to make a journey down to London a number of times a month. It will encourage them to give trains a go.

"The experience of improvements between London and Manchester and London and Liverpool is that people voted with their feet.

"There are now no direct flights from Liverpool to London at all."

Journey times between Glasgow and Birmingham will also be reduced from four hours and 20 minutes to an average of three hours and 58 minutes.

The journey between Glasgow and London is expected to fall even further, to four hours and 10 minutes, in January, with the introduction of a limited-stop service that will only call at Preston.

The engineering works saw the west coast main line rebuilt to take tilting trains travelling at 125mph, with new junctions, platforms and signalling to improve services.

Network Rail said of the project's completion: "The achievement is massive and the result will be a quantum leap in services."

Chief executive Iain Coucher added: "This has been an extraordinarily complex project to rebuild Europe's busiest mixed-use railway. Now it is complete, passengers and freight operators will reap the benefits."

The completion of the works yesterday came after Eurostar, Britain's only high speed rail operator, advised the Scottish Parliament it wanted to introduce a version of the world's newest high-speed train to nearly halve the journey time between Glasgow and London.

The 220mph train, powered by electricity, would cut the trip to two-and-a-half hours, MSPs were told.