The busiest summer break since 2019 is underway – but families hoping to travel by train are facing thousands of cancellations as national rail strikes continue.

The union RMT says 20,000 members working for train operators in the UK have left amid a long and bitter dispute over pay, jobs and working conditions.

The Rail Delivery Group (RDG), which represents train operators, said: “In some areas, only about half of the trains will run, while in others there will be no service at all.” Some trains will run after 7pm.

Negotiations between rail companies and unions have been deadlocked since April, when the RMT rejected offers to pay wages worth 4% each for 2022 and 2023 – subject to reforms in working practices. The agreement was not made available to members. Since then, train operators have announced plans to close most of the station’s ticket offices at English stations.

The union’s general secretary, Mick Lynch, said: “I am proud of our members for showing courage and resolving this long-running dispute.

“The recent attack on ticket offices and the threat of layoffs on our rail lines has generated a huge wave of public support for which we are grateful.

“Our members and unions will not be intimidated by rail bosses or government ministers and our dispute will continue until we can reach a negotiated solution.”

But like independence The leader of Britain’s second-largest railway association, the Transport Employees’ Association (TSSA) has accused RMT of putting jobs at risk by stepping up layoffs.

TSSA general secretary Peter Pendle said: “Because of the direction our colleagues are taking, the agreement – which was a good one – has been dropped and all these changes are being imposed.”

The 24 hours of walking on Thursday coincided with the fourth day of the Aslef train drivers’ latest overtime ban. The union is involved in a similar dispute over wages and conditions.

The last day of Aslef’s work-holiday ban is Friday; on Saturday, July 22, the RMT members went out again for 24 hours.

On the London Underground, a strike called by RMT has the potential to shut down nearly the entire Underground network from Sunday 23 July to Friday 28 July.

The final day of the RMT national rail action is scheduled for Saturday, July 29, with some effects continuing into the next day. And on Monday, July 31, another Aslef ban on overtime begins for six days.

Cricket fans hoping to attend the Fifth Ashes Test between England and Australia in the Oval Office will be swayed by all three groups of industry action.

A spokesperson for RDG accused RMT of “disrupting families’ plans for the summer holidays” and causing “disappointment, frustration and financial stress for tens of thousands of people”.

Elsewhere, driving organizations are warning of congestion at the busiest start to the school holidays in England and Wales.

The RAC predicts the worst traffic jams will come on Friday, with the M5 motorway south of Bristol and the south-west stretch of London’s M25 – between the A3 for Portsmouth and the A22 for Eastbourne – hardest hit.

The AA said: “Those traveling further afield will experience delays around many UK ports and airports this summer.

“Operation Brock was launched in Kent before the summer break.

On the respective Friday of 2022, long lines of people lined up at the port of Dover and the Eurotunnel station at Folkestone as the impact of post-Brexit passport checks became apparent.

As the UK has negotiated to become a “third country”, France’s border police now have to stamp every passport and check the length of stay in the European Union.

Port of Kent chief executive Doug Bannister said: “Once passengers arrive at the port of Dover, they will be cleared through border control – which is expected to take around 90 minutes on peak days.

“However, our modeling indicates that processing times can be up to 2.5 hours during peak hours from 6am to 1pm during the first few Saturdays and Sundays of the summer holidays, due to heavy user traffic these days.”

On Wednesday evening, delays increased at two of the UK’s busiest airports, London Heathrow and Gatwick, with some flights departing near midnight. But the airport was running smoothly on Thursday morning.

Ground handlers working for three companies at London Gatwick are threatening to quit from Friday 28 July in a pay dispute, but members of the Unite union working for DHL – the company that handles easyJet flights – are voting on a new proposal and action affecting the airline has been suspended.