The Labour leadership contest starts in earnest today (18 July) as nominations open for candidates hoping to dethrone Jeremy Corbyn. Former shadow work and pensions secretary Owen Smith and former shadow business secretary Angela Eagle, who both resigned from Corbyn's cabinet in the wake of the Brexit vote, have previously announced their bids.

Corbyn is automatically on the ballot after a ruling from Labour's National Executive Committee (NEC) on 12 July. The grandees' decision means Eagle and Smith will have to attract 20% or 51 signatures from the party's MPs and MEPs.

Nominations will close on Wednesday, with ballot papers being sent out on 22 August and a victor of the leadership race being announced on 24 September in Liverpool. There has been some controversy around who can vote in the election since the NEC ruled that only members who joined Labour before 12 January can have say.

The move comes after Labour's membership surged past 500,000 in the wake of the EU referendum. Corbyn has also criticised the NEC's decision to charge registered supporters £25 ($33) to cast a vote in the election.

The one-off-fee was only £3 in Labour's 2015 leadership election, a ballot which saw Corbyn attract almost 60% of the vote.

Smith, the former shadow work and pensions secretary, officially launched his bid to become Labour leader yesterday after postponing the event because of the terror attack in Nice, southern France, on 14 July.

The Welsh MP warned that Labour were "off the pitch" when it came to providing an effective opposition and alternative government, while promising to re-write Clause IV of Labour's constitution so that tackling inequality is at the centre of its mission. On top of that, he had previously promised to hold a second EU referendum to ratify a Brexit.

"We have a wider gap between the haves and have nots in this country than any of us have known in our lifetimes and it is for the Labour Party, our party, to fight to reduce that gap," Smith declared.

Speaking in his constituency of Pontypridd, Smith added: "Every Labour policy has to be tested against that benchmark: is it going to reduce inequalities in wealth, in power, in outcomes and opportunities, or is it not?

"And if it is not going to reduce those inequalities, then we in the Labour Party should not do it." He is up against Eagle, the former shadow business secretary who reluctantly resigned from Corbyn's top team following the Leave result of the referendum.

The pair appeared on the BBC One's Andrew Marr show over the weekend, where they took part in a so-called 'sofa hustings', and will face Labour's parliamentary party in the House of Commons this evening.

Eagle promised to pull Labour out of "dark times" when she launched her leadership bid on 11 July. "Jeremy Corbyn is unable to provide the leadership that this huge task needs. I believe I can," she said.

"I am not a Blairite, I am not a Brownite and I am not a Corbynista. I am my own woman – a strong Labour woman. I love my party and I love my country. We are at a crossroads and I am ready to lead."

However, it is unclear whether Eagle and Smith will both attempt to be on the leadership ballot because of risking splitting the 'soft left' vote in the party. A single 'stop Corbyn' candidate had been mooted after Labour MPs overwhelmingly backed a motion of "no confidence" against the leader.