As the Christmas getaway becomes more popular, train services to Britain's second-busiest airport are deteriorating because of industrial action and infrastructure problems.

Southern, which runs from London Bridge and Victoria to Gatwick, as well as South London, Surrey and Sussex, has warned of “severe disruption on all dates”.

Even during off-peak spells on a day when no strikes are taking place, dozens of trains between London and Gatwick have been cancelled or severely disrupted.

An overtime ban by Southern drivers has also affected Gatwick Express services, as some Southern drivers also drive Gatwick Express trains. The industrial action is being exacerbated by speed restrictions on the line from Victoria through South London – but many trains on alternative lines, from St Pancras and London Bridge, have also been delayed or cancelled altogether.

Gatwick is served from central London by Southern, Thameslink and the Gatwick Express. Together, they comprise the Govia Thameslink Railway (GTR) train operator.

Passengers using the Southern element of the franchise have been victims of a long-running dispute over whether the driver or guard operates the doors.

Train drivers belonging to the RMT union and Aslef have called a strike on Tuesday 13, Wednesday 14 and Friday 16 December and then for most of the second week of the New Year: Monday 9 to Saturday 14 January.

GTR failed in a legal bid to have the strike called off.

British Airways is warning passengers: “On strike days, no Southern trains will run. Gatwick Express will run a limited service. Thameslink trains are unaffected but will be much busier than normal.”

Mick Whelan, general secretary of the train drivers’ union Aslef, said: “An increase in the number of passengers we are carrying on the railway every day means there are 1,100 passengers on a 12-car train in peak travelling time and just two seconds to check 24 sets of doors and that’s simply not adequate to deal safely and properly with the travelling public.”

Southern guards who are members of the RMT will stop work on Monday 19 and Tuesday 20 December, with a four-day strike across the New Year from Saturday 31 December to Tuesday 2 January.

The RMT union says the dispute is not about pay or conditions, but insists “members are taking strike action and losing pay because they are concerned about passenger safety”.

Gatwick Airport issued a statement warning travellers to “allow plenty of extra time to get to the airport”. It said: “We are expecting significant disruption to rail services to and from Gatwick on 13, 14 and 16 December due to a train drivers strike. There will be no Southern trains and reduced Gatwick Express services.

“The train strike will increase the number of people driving in the area, so roads are expected to be much busier than usual.”

Meanwhile Mick Cash, general secretary of the RMT, has written to the Chief Inspector of Railways alleging that “Southern/GTR are deliberately manipulating events to put the dispute in the worst possible light” by failing to roster available crew.

National Express, which runs coach services to and from the airport, said it has some extra capacity on the strike days.