Downing Street has accused rail, postal and airline workers going on strike of causing “untold misery” and showing “contempt for ordinary people”.

Theresa May’s deputy official spokesman condemned the walkouts in the run-up to Christmas in unusually strong terms on Monday morning, saying the disruption they will cause was “massively unwarranted”.

He suggested the prime minister would not be prioritising further strike laws demanded by some Conservative MPs but refused to rule this out as a possibility if the industrial action gets worse.

Asked about the strikes affecting Southern rail, the Royal Mail and British Airways, he said: “What the prime minister thinks is that the strikes are wrong and that they are causing untold misery to hundreds of thousands of people.

“There are hundreds of thousands of people having their lives disrupted on a massively unwarranted scale by these strikes … If [these strikes] have anything in common, it is shared contempt for ordinary people trying to go about their daily lives … [The unions’] actions are clearly designed to bring about maximum damage and disruption during the festive period.”

CWU members protest outside the Department for Business, Innovation and Skills in London ahead of postal strikes. Photograph: Jonathan Brady/PA

Former cabinet ministers Michael Heseltine and Norman Tebbit are among senior Tory figures who have called on May to take a tough line on trade unions following the wave of strikes and threatened walkouts.

The Unite general secretary, Len McCluskey, said: “The government should be looking at positive ways to resolve disputes, not demonising working men and women who only consider strike action as the very last resort.

“I have never encountered a worker who wants to strike. When they have to take industrial action it is an expression of frustration at not being heard by employers.

“I urge the government to concentrate more on understanding why industrial relations break down, not slinging around threats to remove fundamental freedoms.”

Industrial action by conductors in the RMT union on the Southern rail franchise – coupled with a continuing ban on overtime by drivers in the Aslef union – is expected to bring a second week of havoc to 300,000 passengers between London and the south coast on Monday and Tuesday.

The RMT strikes are part of a long-running dispute over the role of conductors, with further walkouts planned for next month. Aslef has joined the RMT dispute, striking for three days last week and entirely shutting down the Southern network.

BA and Virgin Atlantic also face walkouts over Christmas. Talks aimed at averting strikes by BA cabin crew will be held at Acas on Monday. Members of Unite are due to walk out on Christmas Day and Boxing Day in a dispute over pay. BA said it intended to run a full service on both days despite the strikes.

Alex Cruz, the British Airways chief executive and chairman, said: “We are making sure that this attempt to ruin Christmas for thousands of our customers fails. Over the weekend we have been working on detailed contingency plans to ensure that we are able to operate our normal flight programme from all our airports on both Christmas Day and Boxing Day.”

Cruz said the strike call was causing anxiety among BA’s mixed fleet cabin crew. He said they were seeking to improve the compensation package for mixed fleet cabin crew, who earn a minimum of £21,000 a year for full time work.

There will be talks on Tuesday between the airport services company Swissport and Unite, aimed at averting a 48-hour strike by 1,500 baggage handlers and other airport staff in a dispute over pay, due to start on Friday.

The Post Office is facing possible shutdowns of branches as members of the Communication Workers Union (CWU) strike in a pay dispute.



Last week, Chris Grayling, the transport secretary, told the BBC that he would look at all options to stop rail unions from striking, and while he was not “ruling anything in” he wasn’t “ruling anything out” either.



Lord Heseltine, meanwhile, told the Sunday Telegraph: “You cannot have small groups of people holding society to ransom, regardless of personal inconvenience or cost. It was reported that about 20 MPs had called on Grayling to take action against strikes.

MPs in seats across Southern’s network have faced angry demands for action from their constituents, although the Department for Transport has declined to get involved in the dispute between Southern’s operator, Govia Thameslink Railways (GTR), and the unions.

Labour MPs also appeared to be split over how to handle the dispute. The shadow home secretary, Diane Abbott, has defended unions planning to strike. “Of course these strikes are going to be very disastrous if they all go ahead for the public over Christmas, but people do have a legal right to strike,” Abbott told the Sky News presenter Dermot Murnaghan on Sunday. She added: “It’s not my role to second-guess the decisions of trade union leadership.”

But Meg Hillier, the Labour MP who chairs the public accounts committee, said on the same programme that unions could be shooting themselves in the foot by opting for industrial action over the festive season. “There needs to be a wakeup call about the impact on hardworking people trying to get to work or go on holiday,” she said.



The RMT’s general secretary, Mick Cash, was forced to deny that the union was part of a “Trot conspiracy” after the Sunday Times published a video showing the RMT union president, Sean Hoyle, at a rally saying trade unions were working together to “bring down this bloody working-class-hating Tory government”.



Cash said: “We are a serious trade union dealing with serious issues around safety on the railways. That is our absolute priority. RMT is not party to any Trot conspiracy to bring down government.”