There will be 15 trains a day in each direction, and 10 on Sundays.

The journey will take 70 minutes.

It is nearly 20 years since direct trains last ran between the two cities.

The first train leaves Norwich at 0913 BST.

'Growth centres'

The £10m deal was announced by the MP for Norwich South and Labour Party chairman, Charles Clarke in January 2002.

At the time he said: "It will link two of the most powerful economic growth centres in the region, Norwich and Cambridge, who can mutually benefit by a direct transport link.

"There are already many people who travel between Norwich and Cambridge who now will be able to travel by train.

"If we can reduce traffic on the A11, enable people to go to and from Norwich and Cambridge in comfort, rather than waiting behind the steering wheel, it really will bring big environmental benefits."