This week, news from Westminster is fairly slow as MPs have returned to their constituencies and taken post-election holidays as part of the summer recess. But it's not just our parliamentarians who are hotting up in the sun, Labour's leadership race has ignited.

Jeremy Corbyn's socialist surge from nowhere has sent the party into a tailspin. The left-wing firebrand has carved out a 20 point lead, according to a private poll leaked to the Daily Mirror.

The survey puts Yvette Cooper in second place, but on second preference votes former work and pensions secretary is just two points behind Corbyn. The 46 year old is certainly on a role this week as Alan Johnson, a party favourite and former home secretary, has thrown his support behind Cooper, praising her economic credibility and "inner steel".

Calais crisis continues

Elsewhere, the Calais migrant crisis continues to dog French and UK authorities. Thousands of people have tried to gain access to Britain through the Eurotunnel, forcing French police to keep them at bay with tear gas.

David Cameron has gone on his holidays, leaving foreign secretary Philip Hammond to chair an emergency meeting of the Cobra committee and deal with the situation, which is causing major disruptions to hauliers and tourists.

The UK government had previously promised to give the French £7m ($10.9m) to bulk up security around ports and docks to stop stowaways and Cameron, before taking a break, promised extra fencing and sniffer dogs. However, the Tory administration's response has been criticised on both the left and the right sides of the political spectrum.

Tim Farron, the new Liberal Democrat leader, visited Calais to see the situation for himself and criticised the prime minister's language after Cameron described the migrants as a "swarm". Ukip, meanwhile, have called on the government to draft in the army to support the Border Force as it attempts to process some of the migrants and stop others from reaching Dover.

Cruddas delivers some 'hard truths'

Finally, 'it's the economy what won it' – that is one of the "hard truths" from Jon Cruddas' independent investigation into Labour's miserable general election performance.

The former policy chief warned that voters saw Ed Miliband's party as pushing an "austerity-lite" agenda, but supported the Tories because of George Osborne's promises to tackle the UK's deficit.

The London MP also found that the possibility of a SNP/Labour government, despite Miliband's rejection of coalition with the nationalists, turned the electorate off Labour. 60% of voters in the England and Wales agreed with the statement "I would be very concerned if the SNP were ever in government".

It's important to note that Cruddas' probe is independent and not endorsed by Labour. Margaret Beckett is leading the party's official "learning the lessons" taskforce into the election, which is ongoing. However, with anti-austerity Corbyn in the ascendancy, Cruddas' data may well prove very interesting for Labour supporters and members ahead of the party's leadership election.

David Cameron