Who is threatening to strike, how will affect the London Underground, and what if I already have a train ticket booked? Find out here

As the most disruptive rail strike in a generation approaches, Simon Calder outlines the implications and options for rail travellers.

Q: Just remind us … who’s threatening to strike, when, and why?

The RMT union has called a 24-hour strike of members working for Network Rail, starting at 5pm on Monday. In addition there will be a 48-hour ban on overtime and call-outs on Monday and Tuesday. Network Rail workers provide signalling and maintenance of railway infrastructure across the country, as well as staffing 18 of Britain’s busiest stations. They are involved in a long-running dispute over pay and job guarantees.

Q: The impact if the strike goes ahead?

The train operators have started to outline their plans, and the results are highly variable. The most extreme response is from Virgin Trains on the West Coast Main line. The company has decided than rather than try to run some services and seeing the plans unravel, it has cancelled all its services - between London Euston, Birmingham, Manchester, Edinburgh and Glasgow - on Monday and Tuesday. If the industrial action is called off, some services will be reinstated, but the company says “we cannot be specific at this stage” about what those might be. Its partner Virgin Trains East Coast is planning a skeleton service on both days from London to Leeds, York, Newcastle and Edinburgh, while First Great Western is hoping to operate some services between London Paddington and Reading, Bristol, South Wales, Exeter and Plymouth, but not across the Tamar Bridge into Cornwall.

South West Trains, which is the main operator at Britain’s busiest station, London Waterloo, says there will be a severely reduced service from early afternoon on Monday, with all trains stopped by late afternoon and no services at all on Tuesday.

Q: What about key holiday destinations, such as Cornwall, Wales and Scotland?

Cornwall has no trains at all. Cross Country, which has a vast network centred on Birmingham, and which normally runs to and from Penzance, will only be operating on two small slices of its network: Bristol to Plymouth and Derby to Newcastle.

Arriva Trains Wales says services on a number of routes will not run at all on Monday and only a very few trains will be running on Tuesday.

Transport for London says the vast majority of services will run as normal.

Scotrail will run a few services in and around Glasgow and Edinburgh on Monday and Tuesday, but long-distance links will not run.

Q: And international trains?

Eurostar is likely to cancel four services connecting London with France and Belgium. Rail-sea connections to Holyhead (for Dublin) and Harwich (for Hook of Holland) are unlikely to run.

Q: Will the London Underground be affected?

Transport for London says the vast majority of services will run as normal. However, as some Tube lines rely on Network Rail signals and power supply, if the industrial action goes ahead some services will be affected on Monday, Tuesday and into Wednesday morning: the Bakerloo Line north of Queen’s Park, District Line services to Richmond and Wimbledon, and the Waterloo & City Line.

The London Overground will shut down except for a sporadic service between Dalston Junction and New Cross/New Cross Gate.

Q: What if I have to reach an airport?

The Heathrow Express expects to operate a near-normal service, though with a later start and earlier finish. The Gatwick Express faces severe disruption, as do the two alternative operators between London and the Sussex airport: Thameslink and Southern.

Tens of thousands of people have already bought train tickets

To Stansted, the operator Abellio Greater Anglia is closing down at midday on Monday, and on Tuesday will offer “an extremely limited, skeleton service between London and Stansted airport in the middle of the day”.

Luton airport is faring better, because East Midlands Trains is expecting to operate an hourly service from London St Pancras, as part of a skeleton service to Leicester.

First TransPennine is hoping to run an hourly service from Manchester airport to the city’s Piccadilly station.

Q: I already have a ticket. What are my options?

Tens of thousands of people are in that position. Anyone with an Advance or Off Peak ticket can cancel their trip and obtain a full refund, or travel on Sunday or Wednesday rather than Monday or Tuesday - close to the time of the original trip.

Many ticket restrictions are being lifted for long-distance trains which means that if you have an off-peak ticket to London for Tuesday and want to use it early on Wednesday you are unlikely to face problems.

Q: I have a hotel and show booked in London, but won’t now be able to get there. Can I claim the money back from Virgin Trains?

You can try, but it is unlikely to succeed. Train operators are generally not liable for contingent losses. Neither can you claim under the Delay Repay scheme. The only recompense is to season-ticket holders, who will receive a small refund.