A NEW high-speed train service which promises “faster and more comfortable” between South Wales and London experienced teething problems on its launch today.

Passengers on the Hitachi 800's maiden journey from Bristol to London at 6am saw their train delayed and its air conditioning broken earlier this morning.

A Great Western Railway (GWR) spokesman confirmed the delay was due to a "minor technical matter" that was resolved at the depot.

He said: "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."

He added that the 7am service from London Paddington to Bristol left on time, as did the return service at 9.30am.

The GWR service will make its first journey into Wales on the 11.45 train from London Paddington to Swansea, stopping at Newport on its route.

Trains on the £5.7 billion fleet will reach speeds of up to 125mph upon their initial rollout.

The 10-carriage service has 24 per cent more seating capacity than its predecessor, the High Speed Train, and will boast 40 per cent more seats.

It is expected to cover 803 miles on its first day on the Bristol Temple Meads to London Paddington service.

More than 6,500 passengers will be carried on the train and two further five carriage trains will run as a second 10-carriage service.

The trains will also make use of the electrification work on the South Wales railway line that has been carried out by Network Rail.

Welsh Secretary Alun Cairns was on hand to welcome the 6am train into London Paddington alongside Secretary of State for Transport, Chris Grayling.

And despite the first-day hiccup, Mr Cairns said he was delighted to see the first service of the Hitachi trains roll out.

“From today, passengers across south and West Wales will experience the benefits of travelling on faster, modern trains with increased capacity, greater comfort and better connectivity,” he said.

“The UK Government is investing heavily to build a bigger, better railway for Wales, delivering improved journeys for passengers on the most advanced new trains.

“Passengers expect and deserve high quality rail services. We are committed to using the best available technology for each part of the network, delivering significant benefits for those who use our railways.”