Image copyright Getty Images Image caption Lord Hattersley has said that leaving the European Union would be a "disaster"

Former Labour deputy leader Roy Hattersley has said he supports another Brexit referendum "very strongly".

The politician said Britons have "a right" to have their say on Theresa May's Brexit deal, which goes to a vote in the Commons on Tuesday.

A People's Vote event has been held in Sheffield, with Dame Margaret Beckett and Sir Vince Cable speaking.

Lord Hattersley said those who voted to leave the EU had "no idea" what that would mean.

Former Irish Prime Minister John Bruton has also said that the UK's approach to Brexit meant it had decided to "tear up" the Good Friday Agreement.

Lord Hattersley, 86, who was due to speak at the rally but pulled out due to illness, told BBC Radio 4's Today programme: "I think the British people have a right to cast a vote on the merits of the package Mrs May has negotiated.

"They voted by a small majority to leave the union, but they had no idea what leaving the union meant.

"We now know how bad it will be. We now know that it will be much worse than remaining in, and that the British people have a right to express a view on whether they want to remain in or they want to leave."

'Gutter politics'

He added that "sometimes, you just have to do what is right", rather than looking at what "wins elections" and possibly at the risk of losing Labour supporters.

No deal would be the worst possible scenario and needed to be avoided, said Lord Hattersley, who previously said that leaving the European Union would be a "disaster".

The peer, a minister in the Wilson and Callaghan governments, added that he did not think a general election - which Labour leader Jeremy Corbyn has called for - would happen.

MPs are widely expected to reject Mrs May's deal on Tuesday, negotiated between the EU and UK, with more than 100 Conservative MPs among those expected to vote against it.

Quick guide: What is a no-deal Brexit? A "no-deal" Brexit is where the UK would cut ties with the European Union overnight without a transition period. Theresa May's government, and many others, believe this would be hugely damaging and want a more gradual withdrawal. But if Parliament can't agree on that, and nothing else takes its place, the UK could still leave without a deal. This would mean the UK would not have to obey EU rules. Instead, it would need to follow World Trade Organization terms on trade. Many businesses would see new taxes on imports, exports and services, which are likely to increase their operating costs. That means the prices of some goods in UK shops could go up. The UK would also lose the trade agreements it had with other countries as a member of the EU, all of which would need to be renegotiated alongside the new agreement with the EU itself. Manufacturers in the UK expect to face delays in components coming across the border. The UK would be free to set its own immigration controls. However some UK professionals working in the EU and UK expats could face uncertainty. Some countries, such as Spain, Germany and the Netherlands, have given temporary guarantees about residency status and rights, but there is not yet an agreed policy for UK citizens across the EU in the event of a no-deal Brexit. The situation for holidays and business trips is a little clearer, as the European Commission has said that even in a no-deal scenario, UK travellers won't need a visa for short visits of up to 90 days. The border between Northern Ireland and the Irish republic would become an external frontier for the EU with customs and immigration controls, though how and where any checks would be made is not clear. Some Leave supporters think that leaving without a deal would be positive if the right preparations were made. They say criticism is scaremongering and any short term pain would be for long term gain. But critics - including both Brexit supporters and opponents - say that leaving without a deal would be a disaster for the UK: driving up food prices, leading to shortages of goods and gridlock on some roads in the South East resulting from extra border checks.

Transport Secretary Chris Grayling earlier told the Daily Mail that not leaving the EU would cause the 17 million people who voted for Brexit to feel "cheated". He said blocking Brexit could lead to a surge in far-right extremism.

Lord Hattersley dismissed those comments, saying not many would regard Mr Grayling as "an expert in these matters".

Pro-EU former Conservative minister Anna Soubry also criticised Mr Grayling's comments as "irresponsible nonsense".

David Lammy, a Labour former minister, said it was "a desperate attempt by a government minister to use a tiny far-right minority to hold our democracy to ransom", adding: "It is gutter politics."

Image copyright PA Image caption An anti-austerity march took place in central London, ending with a rally in Trafalgar Square

Ms Soubry was also among those at the Sheffield rally. Lord Hattersley had been due to say that the "vast majority" of Labour members want the party to campaign for a new Brexit referendum if hopes of an early general election are extinguished.

He was to say that "no conceivable deal which is remotely as beneficial to Great Britain as full membership of the European Union" and that young people would pay the price for Brexit.

Meanwhile, hundreds of people have been attending an anti-austerity march in central London.

The event was organised by The People's Assembly Against Austerity, with speakers including shadow chancellor John McDonnell.

People gathered outside the BBC's New Broadcasting House before marching to Trafalgar Square, many wearing yellow vests - which national organiser Ramona McCartney said was to show "solidarity with the left and working class in France".

France has seen weeks of anti-austerity demonstrations by those wearing the vests, known as the "gilets jaunes" movement.

Addressing protesters in Trafalgar Square, Labour's John McDonnell said eight years of austerity was "tearing apart the very social fabric" of the UK.

He said when "the time is right", his party will move a motion of no confidence in the government. He read a message from Mr Corbyn, saying a general election was needed to bring about a "fairer, more equal society".

An anti-austerity protest also took place in Belfast city centre.

Separately, there was a march in central London which was broadly pro-Brexit, BBC home affairs correspondent Daniel Sandford said, but smaller than the anti-austerity rally, with between 200 and 300 attending.