A £100 million project to fully refurbish 268 diesel and electric trains run by Northern rail is underway.

The company's engineering team, together with experts from external specialists, is undertaking the ambitious programme at six train depots across the country.

Bosses have lifted the lid on the painstaking process.

On average it takes 120 work-hours – roughly five full days – to renovate just one carriage and requires the input of around 20 experts in their respective fields, including electricians, painters, vehicle builders, welders, textile fitters and project managers.

The entire transformation project is expected to use more than half a million metres of cabling (enough to reach from Manchester to Amsterdam), 672,000 nuts, screws and bolts and more than 100 tonnes of new equipment.

The refurbishment of the 268 trains (well over 600 carriages) is expected to take more than 72,000 work-hours, equivalent to 3,000 full days or just over eight years.

Northern say they are committed, where possible, to using suppliers based in the north of England.

Andrew Marden, head of engineering transformation at Northern, said: “This transformational engineering programme is absolutely mammoth and the complexity of giving 268 a new lease of life is extremely challenging.

“The refurbished trains will massively improve our customers’ experience and the units will have all the facilities that you would expect from a brand-new train. Customers will hardly be able to tell the difference.

“Of course, we have a really difficult balancing act to keep services operating whilst carrying out the improvement work and are aiming to complete the renewals as quickly as possible.

“Our engineering teams are fantastically skilled in a variety of disciplines and are making great progress in delivering enhancements for our customers.”

Each refurbished train will include better seating, fully accessible toilets (including baby changing facilities), free wifi, digital customer information, better lighting and security focused CCTV.

The refurbished trains will have new flooring and an external repaint.

On-board systems and engines will also be completely renewed to improved service reliability and modernise maintenance.