Len McCluskey has launched a broadside against the government for “demonising” workers who consider strike action only as a last resort.

The Unite general secretary spoke out as Downing Street claimed industrial action this week on trains and in post offices and airports would cause “untold misery” and showed “contempt for ordinary people”.

McCluskey criticised Theresa May, following comments by her official spokesperson, and said: “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,” he added, in response to rumours that the government are looking at toughening anti-strike laws.

Gerard Coyne, the secretary of Unite in the West Midlands who is competing against McCluskey for the top job at Unite, criticised Meg Hillier, the chair of the public accounts committee, after she said unions needed a “wake-up” call about the impact of the strikes.

Coyne said: “I was angered to read the statement made by Labour MP Meg Hillier and particularly disappointed by her claim that the current industrial disputes should act as a ‘wake-up call’ for unions. It is the management of these companies that need to wake up and Southern Rail, in particular, must take responsibility for its own appalling record of service, which its long suffering customers have had to endure for too long. Meg Hillier should acknowledge that industrial action is only ever a last resort and that management must urgently sit down and negotiate with union representatives who are eager to settle these disputes.”

Dave Ward, the general secretary of the CWU, the union representing striking crown post office workers, told Good Morning Britain the country has “the worst anti-union legislation anywhere across Europe”.

Workers need “more rights not less”, he added, and highlighted Tory policies which have left the post office in “crisis” alongside other services such as the railways and the NHS.

Frances O’Grady, the general secretary of the TUC, told the BBC she had “enormous sympathy” with passengers and staff but expressing concern over another “agenda”.

Some MPs are demanding “even more draconian laws” against trade unions, following the Trade Union Act, she said.

She criticised the arguments of Tory MP Chris Philp, who argued against because of the impact on the passengers’ commute, saying: “They’ve been unable to get to work for the whole year because of Southern’s performance”.

It was also announced today that Usdaw members working at Weetabix are planning strike action in the new year in response to proposals to alter shift patterns.