Labour's bitter leadership battle descended toward farce today as challenger Owen Smith asked Jeremy Corbyn for the right to address his packed rallies.

Mr Smith is facing a steeply uphill battle to dislodge the veteran left-winger and today admitted he was the 'underdog' in the leadership contest.

The former front bencher admitted his hopes had suffered another blow on Monday when the High Court overturned a 'freeze date' on when Labour members gained the right to vote in the contest, adding 130,000 people to the 'selectorate'.

On another front of the Labour battle, a row between Mr Corbyn and his deputy Tom Watson also escalated today as Mr Watson urged his boss to join him in condemning 'entryists' to the party.

And the chaos in the party has also raised fears the autumn conference might have to be cancelled because union concerns mean the event does not yet have an agreed security contractor.

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Owen Smith, pictured tonight on ITV News, urged Jeremy Corbyn to let him address the mass rallies the Labour leader has gathered to support him as he defends his job

Mr Smith tonight told ITV News: 'I don't know what the split is going to be (in the 130,000 additional members).

'I think it's probably going to be in Jeremy's favour. It's very clear that I'm the underdog in this.

'I'd really like to go to some of those momentum rallies with Jeremy. I've asked him to let me attend and speak to the great masses he's drawing from the momentum movement.

'I think that would be really good. It should be an open democratic contest.'

Mr Watson was slapped down by the Corbyn campaign yesterday for 'peddling baseless conspiracy theories' after he warned in a Guardian interview about 'Trotskysist' interference.

The deputy leader today produced a dossier of evidence about hard-left involvement in the Labour grassroots.

And in a letter to Mr Corbyn, Mr Watson said: 'For the avoidance of doubt, I am asking you to confirm you believe members of the Socialist Party and the Alliance for Workers Liberty should not be allowed to be members of the Labour Party given the proscription of these two groups (then called Militant and Socialist Organiser) by annual conference during Neil Kinnock's leadership.'

Labour leader Jeremy Corbyn is facing a major rebellion from MPs who say he is not fit to be in charge of the party

The 2016 annual conference is due to begin on Saturday September 24 in Liverpool but appeared to be under threat of a humiliating cancellation today.

Labour's ruling National Executive Committee (NEC) voted to boycott G4S last year over commercial links to Israeli prisons.

But leaked emails to Iain McNicol, Labour's general secretary, reveal that a replacement provider has yet to be found.

The issue surfaced as the battle for control of Labour intensified again.

Allies of Jeremy Corbyn are said to be preparing an effort to oust Mr McNicol if - as is widely expected - their man defeats the current leadership challenge from Mr Smith.

Peter Taaffe, the former leader of the hard-left Militant group pushed out by Neil Kinnock in the 1980s, poured fuel in the flames today by saying he expects to be readmitted to Labour if Mr Corbyn wins again.

'People say: you were a long time gone, welcome back,' Mr Taaffe told the Guardian. 'I know Jeremy, he's a good bloke. He's principled. He's on the left.'

On another front of the Labour battle, Tom Watson today sent Jeremy Corbyn (pictured together at last year's conference) a dossier on hard-left entryism to Labour after Mr Corbyn's campaign yesterday accused him of 'peddling baseless conspiracy theories'

However, Labour MP John Spellar told MailOnline it would be a disaster if the left-winger was readmitted.

'Peter Taaffe is a dedicated professional revolutionary who only wants to use the Labour Party for the purposes of Militant,' he said.

'I think people like Peter Taaffe emerging who have such a very very clear record, I think that makes very clear what they are trying to do.'

Meanwhile, Mr Smith was boosted by an endorsement from the GMB union, with members voting by 60 per cent to 40 per cent in his favour.

Labour is already facing the prospect of going into the conference with its leadership still hanging in the balance.

A High Court ruling this week potentially making another 130,000 people eligible to vote in the contest between Jeremy Corbyn and Owen Smith is threatening to derail the timetable.

The party has now approached five other security firms, according to The Times, but three declined the contract and one withdrew after a risk assessment.

Former frontbencher Owen Smith is challenging Jeremy Corbyn for the Labour leadership

The last remaining option is said to be Showsec, which is embroiled in a bitter row with the GMB.

A senior Labour source indicated that a deal had still not been finalised for the gathering in Liverpool next month.

But they insisted the party was 'absolutely confident that arrangements for security will be in place and Conference will go ahead as planned'.

The email written by Labour's deputy treasurer Simon Mills and seen by the Guido Fawkes website said that the party was 'in the very difficult position of having to appoint a potentially anti-union organisation'.

Allies of Mr Corbyn are said to be preparing to remove General Secretary Iain McNicol from his post if they win the leadership election

'We do not have other options to pursue and are under pressure from the Home Office to make an appointment very soon,' the letter said.

'It must be noted that should we be unable to appoint a security contractor it is within the power of the Home Office/police to stop conference taking place.'

Labour MP John Woodcock said that the issue was making the party a laughing stock.

'This is just another example of the ideologically purist leader's team creating havoc for ordinary party members with their selectively and suspectly applied principles,' he told The Times.

'They are imposing this decision, made from their bunker in central London, on party members just at a time when the threat levels to non-Corbyn supporters are increased because of harassment.

'They have managed to screw up even the most basic and decent thing as providing security for us and risk making Labour a laughing stock.'

As well as leaving Labour with a security crisis, the boycott further riled the party's pro-Israeli MPs. Since the far left gained control, Labour's once-warm relationship with the Israeli Labour Party has rapidly fallen apart.

Mr Smith this afternoon welcomed GMB's endorsement, which came after a ballot of its members.

GMB leader Tim Roache said the Labour Party was at a cross roads as he endorsed Owen Smith for leader after a ballot of members

Mr Smith said: 'At the heart of my campaign are commitments to strengthening our trade unions, ending exploitation and delivering greater equality.

' It's a great honour to receive GMB's nomination to be the next leader of the Labour Party after a consultation with its members.

'I look forward to working with the GMB, its members and all in the labour movement to tackle inequality, invest in strong public services, and for Britain to have trade union and workers' rights that are the envy of the world.'

General secretary Tim Roache said: 'The Labour Party is at a crossroads. I'm under no illusions that we're living through dangerous political times - the like of which I haven't seen during my three decades in our movement. It's time for us to face up to reality.