Up to 12,000 maintenance workers in the Rail Maritime and Transport Union will remain on strike after walking out at noon on Saturday in a row over jobs and conditions.

NR said there had been no effect on trains and services across the UK were running as normal.

But the union had warned that the industrial action would have a cumulative effect and could impact on services.

NR took maintenance work back in-house four years ago from seven private companies and inherited more than 50 different sets of terms and conditions.

The company said the union had been making "ridiculous" demands including putting all workers on a 34-hour working week and increasing pay by "massive" sums, which could add more than £100 million to the maintenance wage bill.

Some maintenance work has been rescheduled as a result of the strike