Railway operator GWR has confirmed the impact that the upcoming railway strikes will have on its ability to operate a service.

The Aslef union has announced strike action that will affect rail services on Friday 12 May, Wednesday 31 May and Saturday 3 June, and the RMT has announced strike action that will affect services on Saturday 13 May.

In addition, there will be further disruption from Monday 15 to Saturday 20 May and on Saturday 13 May and Thursday 1 June due to industrial action short of a strike. This action short of strike is likely to cause some short-notice alterations or cancellations.

On the strike days a reduced, revised timetable will operate across several train operators, including GWR. Many parts of the GWR network will have no service at all. Services will start later and only operate for a limited period during the day.

A spokesperson for Great Western Railway (GWR) said: "If you intend to travel where trains are running, please check before you travel. Trains that are operating will be busier than usual because we will not be able to offer the normal service frequency. Other train operators are also affected by this action, so onward travel could also be affected.

"Where we are able to run services, they are expected to be extremely busy and we are not able to provide bus replacement services.

"Customers who have already purchased tickets for strike days can claim a full refund or amend their ticket; those who travel and are delayed may be entitled to Delay Repay  compensation if they are delayed by 15 minutes or more."

The spokesperson added: "To help customers, tickets will be valid for travel on alternative days on GWR services as follows:

Thursday May 11

Trains are set to run as planned with some minor changes to late-night services. There will be no night riviera sleeper service.

An extremely limited service will operate. There will be a reduced operating window; services will start at 07:30 and must be completed by around 18:30. If you intend to travel where trains are operating, please do check both outward and return journeys.There will be a limited rail service between Plymouth and Gunnislake.

No railway services will call at Saltash, St Germans, Menheniot, Liskeard or Bodmin Parkway.

No railway services will call at any stations on the Liskeard to Looe line, the Okehampton to Exeter St Davids line or other Cornwall branchlines with the exception of the above. The Night Riviera Sleeper service will not operate.

An extremely limited service will operate. There will be a reduced operating window; services will start at 07:30 and must be completed by around 18:30. If you intend to travel where trains are operating, please do check both outward and return journeys.

There will be a very limited service between Penzance and Plymouth - including Saltash, St Germans, Menheniot, Liskeard or Bodmin Parkway.For onward connections, passengers will be required to change at Plymouth for limited services to London Paddington and Bristol Temple Meads.

There will be no services on any Cornish branchline, and there will be no service on the Okehampton to Exeter line.

Trains will run as planned with some minor changes to service start-up. Please check before you travel.

The Night Riviera Sleeper service resumes.