JAMES FORSYTH: It's Dave's summer barbecue - with Labour on the grill 

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On Wednesday, David Cameron got the entire Cabinet, plus Boris Johnson, down to Chequers for an end-of-term catch-up. After the formal session in the morning, he invited everyone to eat outside.

The lunch was a chance to show off one of Cameron's most prized possessions – the Obama BBQ.

The £1,300 gift from the President is even personalised with a Union Jack and a Stars and Stripes. But just as everyone was scoffing their lamb burgers, sausages and salad, a rainstorm sent them scurrying back inside.

'We mustn't believe Corbyn's going to win.We must believe the madness will pass,' one aide said

It takes more than a little downpour to dampen Tory spirits these days, however. Ten minutes later, they were back outside in the sun for their strawberries and cream and basking in the warm glow of Labour in meltdown.

For the Opposition are in the middle of the most disastrous leadership contest in living memory. Tories can barely contain their glee that the shock new frontrunner is Jeremy Corbyn, a throwback to the days of the loony Left.

'Nobody can quite believe it', one Secretary of State tells me.

As the assembled Ministers discussed a presentation on the Labour leadership race from Downing Street aide Adam Atashzai, they tried desperately to keep their feet on the ground.

'We mustn't believe Corbyn's going to win. We must believe the madness will pass,' one told me, adding: 'We've got to assume that the next leader will be Andy [Burnham] or Yvette [Cooper] and plan on that basis.'

'Total utter terror' is how one veteran Labour campaigner sums up the mood in his party.

He warns that defeating Corbyn 'isn't about saving the next Election. It is about the Labour Party's very existence'. Why are Labour in a blind panic? Because the possibility of a Corbyn victory is all too real.

'It is a two-horse race and it is going to be close,' concedes one confidant of the previous frontrunner Burnham.

In fact, it may already be too late to stop Corbyn, according to one of those who has helped run a previously successful Labour leadership campaign. 'There is not much time on the clock to make up a lot of ground on a popular frontrunner,' warns the source, pointing out that the ballot papers go out in just three weeks.

'It is a total mistake to say this will go away because it has to.'

Corbyn's rivals are desperately hoping the darling of the Left won't be able to survive the scrutiny that is coming his way. But even if he falls at the last, the Corbyn phenomenon is doing real damage to the party.

One Cameron ally argues that it says something about today's Labour Party that there will be 'more votes for the candidate who is pro-Hamas than pro-business'. And as the row over welfare shows, the Corbyn tendency is dragging the party ever further from the Centre ground.

As the other candidates desperately try to shore up their Left flanks, the Tories are taking careful note of everything they say.

'Certain loose words that have been used, we can hang round their necks,' crows one Tory.

But most worrying of all for Labour is the failure of the other candidates to put Corbyn to the sword. Corbyn is no Tony Benn. He isn't a charismatic orator or a brilliant media performer. He's a bog-standard, old-fashioned, dyed-in-the-woolly-beard Left-winger. But he's still running rings around them. If Burnham and Cooper can't rally their own party behind them, what chance do they have of winning over the country?

...But guess who ended up sitting next to Theresa

Boris was put next to Home Secretary Theresa May, who had humiliated him in the Commons earlier this month

Boris Johnson's invitation to the Cabinet get-together at Chequers was meant to be an olive branch from Downing Street to the London Mayor after a difficult few weeks.

But whoever was doing the seating plan was in a mischievous mood. Boris was put next to Home Secretary Theresa May, who had humiliated him in the Commons earlier this month with her announcement that she would not allow the Metropolitan Police to use his water cannon.

Boris, pictured left with Mrs May, took this in good humour, I'm told, quipping that everyone might need hosing down.

But relations are so sensitive that David Cameron's team went out of their way to stress they weren't in charge of the placement. They pointed the finger at a civil servant with a rather wicked sense of humour.

As David Cameron heads to the Far East to promote British goods, he'll fly the flag in a rather unprepossessing jet.

I'm told that Downing Street looked into hiring a rather more luxurious aircraft with a special executive section, but they were beaten to all the available ones by the Premier League football teams heading east on their pre-season tours.

It's a reminder for Cameron, if he needed one, that there are a fair few Premier League exports who can command a bigger audience than he can.

Lynton Crosby masterminded the Tories' first outright Election victory in 23 years, but he isn't done yet. On Monday, he turned up in Parliament's Portcullis House to tell Tory MPs why people had voted for them.

In a demonstration of his influence, the Prime Minister, the Chancellor and the Chief Whip all turned out to hear his latest poll findings.

First, he pointed out that only one in ten voters had backed the Tories because of the local candidate, and a far higher number did so because of Tory policies. In other words, MPs shouldn't forget what got them to the Commons in the first place. Crosby then set out what the voters remember the Tories talking about. The economy was top of the list, followed closely by Europe. He said voters associated the Tories with 'performance measures' such as managing the economy and competence.

So far, so reassuring. But it was the next slide that had MPs squirming. Crosby asked voters what Tory promises they remember and the most popular was 'controlling immigration'.

Oh dear. This is what the Tories spectacularly failed to do in the last Parliament.

It was a timely reminder why David Cameron needs to make regaining control of our borders part of the EU renegotiation.

Or, as a straight-talking Aussie like Crosby might say: 'It's time to get a bloody grip, mate.'

Quotes of the Week 

'When people say, 'My heart says I should be with that politics', well get a transplant.'

Tony Blair warns that Labour risks being out of power for years if it elects Left-winger Jeremy Corbyn as leader.

'It could have been a lot worse.'

Tracey Leach, after her son Brock, 14, survived a 100ft cliff fall AND being bitten by an adder in Cornwall.

'It does my nut in. You're on the phone and you have to get your sentences out between bongs.'

SNP's Mhairi Black has only been an MP for two months and is already irritated by Big Ben.

'We don't have recipes in it for falafel or anything like that.'

Actress Tilda Swinton - famous for her porcelain skin, has a tandoori tan, in her latest film role

'This woman looks like a lot of women I pass in the street every day - tandoori tan, the eye make-up and hair. But for me that look is extreme.'

Actress Tilda Swinton - famous for her porcelain skin - is unrecognisable in her latest film role. 

Simon Keegan, of online magazine Martial Arts Guardian, is bemused by The Guardian newspaper's claim that readers might confuse the two publications.

'Today the Earth is a little less lonely because there's a new kid on the block.'

Nasa analyst Jon Jenkins, as scientists discover an Earth-like planet – a mere 1,400 light years away.

'The studded leather mini-dress looked good from a distance… of, say, 200 miles. Up close it would frighten a gargoyle.'

Writer Kathy Lette, recalls one of her fashion disasters.

'DNP: do not purchase, do not partake, do not please, death's not pleasant.'

Fiona Parry, whose daughter Eloise, 21, died after an accidental overdose of diet pill DNP.

'We had to choose between plague and cholera.'

Finnish politician Tino Soini explains why his country backed another bailout for Greece.

'She is probably thinking, 'If this goes in I'll get a new kitchen.' 

Golf commentator Peter Alliss sparks a sexism row with his remarks about Kim Barclay, below, the wife of The Open winner Zach Johnson.

Golf commentator Peter Alliss sparked a sexism row with his comments about Open Winner Zach Johnson's wife Kim Barclay