A 41-MINUTE delay and faulty air conditioning marred the launch of a new fleet of trains costing £5.7 billion.

The first passenger service by the new Hitachi-built Intercity Express trains was disrupted as it travelled from Bristol to London on Monday morning.

It was due to leave Bristol Temple Meads at 6am but did not set off until around 6.25am, according to rail website Realtime Trains.

The Great Western Railway service, which was carrying Transport Secretary Chris Grayling, industry bosses and regular commuters, arrived at London Paddington 41 minutes late.

During the journey passengers reported a leak from an air conditioning unit.

A GWR spokesman said: "Unfortunately, the train was delayed this morning due to a minor technical matter that was quickly resolved at the depot.

"These trains have been running successfully on UK tracks for over two years and recently passed the industry standard 5,000 miles running without a fault.

"Hitachi will be investigating this matter thoroughly."

Hitachi said in a statement: "The Bristol to London service experienced a few technical challenges, for which we apologise to passengers for any inconvenience caused.

"We are of course disappointed with an issue with this train's air conditioning and water ingress in one of the carriages. We are investigating this as a matter of priority and will restore the train back into passenger service once fully rectified."

Some 122 of the new Class 800 Hitachi trains are due to be in service on GWR and Virgin Trains East Coast services by 2020, replacing the Intercity 125 fleet.

They are capable of running at 140mph, although will be limited to 125mph without tracks being upgraded.

The trains will also have to switch from electric to diesel power from Maidenhead to Bristol due to Network Rail's delayed project to electrify the route.

More than 4,000 extra seats into London Paddington during the morning peak will be available from next year, with an additional 12,000 seats into London King's Cross available by the end of 2020.

Mr Grayling said: "This Government is investing record amounts to modernise Britain's rail network and give passengers the faster, more comfortable trains and the better journeys that they expect.

"These new state-of-the-art trains show our commitment to put passengers at the heart of everything that we do."