Network Rail is advising passengers on Transport for Wales services to only travel if it is “absolutely necessary” during rail strikes later this week.

The National Union of Rail, Maritime, and Transport Workers (RMT) and the TSSA union have announced strike action will take place on Thursday, August 18 and Saturday, August 20 – with severe disruption expected again across the whole of the UK with many routes completely closed.

This will be the third major rail strike this summer as the dispute between the unions and Network Rail over pay, planned redundancies and working conditions continues to be unresolved.

Whilst Transport for Wales is not involved in either dispute its services will be affected, as it relies on Network Rail staff to run trains on much of the network.

Transport for Wales said in a statement that “specially trained and fully qualified back-up staff will again step in during the walkout to keep vital services running” but the company is advising people not to travel unless it is “absolutely necessary”.

Only 10 per cent of rail services will run on Transport for Wales' network on the strike days, with services beginning later and finishing earlier than usual.

On the strike days Transport for Wales will run an hourly service between Cardiff and Newport. Hourly services will also run on the Core Valley Lines – between Cardiff Central and Rhymney, Treherbert, Aberdare and Merthyr Tydfil.

Great Western Railway will run a reduced number of trains between Cardiff and London Paddington on the strike days but no Great Western Railway services will be able to operate west of Cardiff.

Passengers are also being warned that there is likely to be some disruption on the days after each strike – Friday August 19 and Sunday August 21 – as workers return to duties.

Nick Millington, acting route director at Network Rail Wales & Borders said: “We’ll be running as many services as we safely can for those who absolutely need to travel by train, but we are urging everyone to plan ahead, check their journey and expect severe disruption.”