Image copyright EPA Image caption Unions have said they will fight the government "tooth and nail"

Controversial plans to tighten rules on trade union strike ballots in Britain have passed their first Commons hurdle despite fierce Labour criticism.

MPs backed the Trade Union Bill, which proposes higher voting thresholds for ballots, by 33 votes at second reading.

Business Secretary Sajid Javid said the bill was "not a declaration of war" against unions but necessary to stop "endless" threats of industrial action.

Labour said the bill was "draconian and counter-productive".

The second reading in the Commons is the key test of whether legislation is likely to get through a vote of MPs - but the bill now has to go through a lengthy stage of line-by-line scrutiny in committee and also needs to be passed by the House of Lords before getting its final Commons approval.

New Labour leader Jeremy Corbyn and his shadow chancellor John McDonnell were present on his party's frontbench for the first time as MPs debated the proposals.

Media playback is unsupported on your device Media caption Sajid Javid insisted the reforms to trade unions were "not an attack on the rights of working people".

The government wants to impose a minimum 50% turnout in strike ballots - with public sector strikes also requiring the backing of at least 40% of those eligible to vote.

Under current rules, strikes can be called if the majority of those taking part in a ballot vote in favour.

The bill, which would apply to unions in England, Wales and Scotland, will also:

Double the amount of notice unions have to give before a strike can be held - from seven to 14 days

Allow employers to use agency workers to replace striking staff

Introduce fines of up to £20,000 on unions for repeatedly failing to ensure picket supervisors wear an official armband

End the so-called check-off system for collecting union subs direct from a salary

Addressing MPs, Mr Javid rejected claims that the law would make it "illegal or impossible" for unions to go on strike, saying they would still be able to do so when they made a "compelling case" for action to their members

"This bill is not a declaration of war on the trade union movement," he said. "It is not an attempt to ban industrial action. It is not an attack on the rights of working people. It won't force strikers to seek police approval for their slogans or their tweets."

The bill was designed to protect the low-paid and self-employed by making it harder for prolonged industrial action to be triggered by a "handful of workers", Mr Javid said, arguing the measures were broadly backed by the public.

He added: "At the heart of this bill, it is all about democracy and accountability."

Media playback is unsupported on your device Media caption The general secretary of the Trades Union Congress warned the reforms could "poison industrial relations"

In passionate exchanges in the Commons, the bill was backed by a succession of Conservative MPs, with Mayor of London Boris Johnson saying he could find no fault with the "serious and sensible" measures.

"It is utterly wrong that public workers should be subject to intimidation on the picket line," he said. "As a result of intimidatory behaviour we have seen strikes triggered by a tiny minority that have caused far worse disruption and have caused inconvenience and misery for millions."

But it was labelled as "vindictive" by Green MP Caroline Lucas, while Labour's Dennis Skinner told ministers "to get rid of it".

"This bill is opposed by all unions affiliated to the Labour Party, to all unions not affiliated to the Labour movement and even the Royal College of Nursing has said no to this bill," he said. "It is a travesty and an intrusion into the democracy of the workplace."

Image copyright AP Image caption London Underground workers have held a series of strikes in recent weeks

And the new shadow business secretary Angela Eagle said she was "dismayed" that the government was intent on "attacking trade unions rather than working with them in social partnership to improve economic efficiency and productivity".

Conservative MP David Davis said he would vote for the bill on Monday but could oppose it at a later stage unless his concerns were addressed.

"I particularly am offended by the idea that a picket organiser needs to give his name to the police," he said.

"This to me is a serious restriction of freedom of association... It's not on the same basis as let's say getting the organiser of a big demonstration to give his name to the workforce. There's all the difference in the world between half a million people clogging up London and half a dozen pickets standing around a brazier shivering whilst they are trying to maintain a strike."

'Suppressing rights'

TUC general secretary, Frances O'Grady, told the annual TUC Congress in Brighton that the bill was the biggest attack on unions in 30 years.

Speaking to BBC Radio 4's Today programme earlier, Ms O'Grady said the bill threatened "the very principle of the right to strike" and will allow employers to "bus in agency workers to break a strike".

"I think Acas [Advisory, Conciliation and Arbitration Service] has certainly pointed out the danger that if you suppress that right for people who feel they are being unfairly treated at work to democratically take strike action, then people will find other ways to express that discontent," she said.

The GMB's Sir Paul Kenny said he would be prepared to go to prison if measures such as fining pickets for not wearing an arm band become law, while Unison's Dave Prentis said his union would withdraw from partnership working in the NHS if the bill became law, a move he said would affect talks on issues such as equal pay.