TESTING of a £500m fleet of new trains has been partially halted after a fault was discovered.

A problem was found in Northern’s 98 trains, built by Spanish train manufacturer CAF in Irun and Zaragoza, which have been undergoing testing since the first unit arrived in the UK in late 2018.

The Bolton News understands that a problem with the coupling mechanism which connect one unit to another caused engineers to become concerned about the cornering on sharp bends.

At a meeting of the Bolton Rail Users Group, regional director Chris Jackson, explained that the couplers were "essentially too large" and were sometimes catching on the body of the train as it went around corners.

As a result, UK testing of the fleet has been postponed, while Northern individually fixes each train. It is unknown whether this will affect plans to introduce the new stock across the network over the coming months.

The arrival of the first of the new units in the country in October was seen as a “landmark” moment for the under-fire train company They are expected to represent a major change for passengers with features such as free customer Wi-Fi, air conditioning, at-seat power and seat reservation system.

The £500m deal included 55 diesel units and 43 electric units. These are split between a range of different formations, with 25 two-car, 61 three-car and 12 four-car set ups.

The new stock is expected to aid Northern in removing the widely-disliked Pacer trains, which were first introduced more than 30 years ago.

The company still uses the trains on a number of lines, including running regular services between Bolton and Manchester.

Northern says it will have taken all Pacers away from the network by the end of the 2019 as it phases them out in favour of new and refurbished electric and diesel stock.

This is due to begin on May 19, a year after a chaotic timetable change caused serious problems for Bolton’s commuters.

At the same time that the old units are being removed, more electric trains will be seen on the newly electrified lines through the borough. This is part of an effort to increase capacity and reduce the number of delays and cancellations.