A bitter row has broken out over the rail dispute after the leader of the drivers’ union branded the Transport Secretary a liar.

Grant Shapps tweeted that passengers using Avanti West Coast services should expect disruption on Sunday because of unofficial strikes.

But Aslef hit back, saying there was no action on Sunday, accusing the minister of lying.

Mr Shapps tweeted: “UNOFFICIAL STRIKES: Passengers using Avanti West services should expect disruption today. Archaic rules from 1919 mean working on rest days is voluntary. Unions now stopping drivers volunteering – causing misery for public & staff who won’t get paid. We MUST modernise rail.”

Mick Whelan, general secretary of Aslef, said: “Grant Shapps is a liar. He is not only wrong, he knows he is wrong.

“His propensity to lie is just one reason why he could not get enough backers to get in the ballot to become Tory party leader. That and the fact that he is not very good at his job.

“The truth is that the company does not employ enough drivers to deliver the services it promises passengers it will run. The company, and the minister, should stop lying and start recruiting.”

Aslef members at Avanti will strike on August 13 as part of the long-running dispute over pay and conditions, but the union said no action is being held before then.

Avanti West Coast said unofficial action by drivers means it is facing “multiple short-notice cancellations” on its network from Monday.

The firm said in a statement that cancellations are likely to continue until the current industrial dispute is settled.

“Customers are urged to check their journey on our website before coming to the station, and should be prepared for services to be disrupted at short notice and be very busy.

“We are sorry for the enormous frustration and inconvenience this will cause our customers and condemn the drivers’ actions.

“We urge them to engage in meaningful talks around modernising working practices and developing a railway fit for the 21st century.”

A union spokesman said the company does not employ enough drivers to deliver its services.

Aslef members at seven train companies went on strike on Saturday, causing huge disruption to services.

More strikes are planned in August by Aslef, the Rail, Maritime and Transport union and the Transport Salaried Staffs Association in worsening rows over pay, jobs and conditions.

An Avanti spokesperson added: ”We have a long-standing agreement with drivers for them to work shifts as overtime.

“The drivers like this as they earn extra money. Normally there are circa 250 trains a week covered by this arrangement, with a pool of extremely reliable drivers that sign up regularly and without issue.

“Literally overnight, the number for this week has dropped to fewer than 10 trains covered by overtime. The drivers have, en masse, withdrawn their volunteering.”