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Jeremy Corbyn is preparing a major power grab to seize full control over the Labour Party machine in the wake of the general election, the Evening Standard can reveal.

Major changes to the party rulebook are to be put to a conference vote this autumn, offering more seats on the ruling National Executive Committee to constituency Labour Party (CLP) branches.

Another vote is expected on changes to the leadership rules that would allow grassroots members and trade unions to put a Left-winger’s name on the ballot paper in future — abolishing the effective veto held by Labour MPs at Westminster.

Officially, the moves will be driven by activists submitting motions to party conference rather than by the leadership. But shadow cabinet members close to the Labour leader have confirmed to the Standard that he favours them. The disclosure comes a day after Mr Corbyn sacked three frontbenchers who took part in a revolt of 50 Labour MPs against a “hard Brexit”. The dismissals signalled a tougher line against infighting and open dissent in the wake of his better-than-expected general election success.

One of those fired, former shadow housing minister Andy Slaughter, accepted the decision this morning. “I voted against the whip and was sacked, which was entirely appropriate,” he said. “That’s the norm.”

Hammersmith MP Mr Slaughter was among rebels who before the election escaped without punishment for voting against triggering Article 50 to leave the EU. But the post-election approach was stricter, he said.

“There was a slightly different atmosphere before the election and so people were given a bit more leeway. That was the exception — this is the rule.”

Mr Corbyn is planning a summer of intense campaigning to take advantage of his increased popularity, which saw him feted by a 150,000-strong crowd at the Glastonbury Festival on Saturday. Tomorrow he will kick it off by marching into Tory marginal Hastings and Rye, where Home Secretary Amber Rudd has a majority of just 346.

Next weekend he travel to Labour’s traditional heartlands, attending the Durham Miners’s Gala, before visiting the annual Tolpuddle Martyrs festival in Dorset a week later.

But the test of his enhanced authority will come at party conference when the new rules are expected to be put to a vote. They include:

Creating extra seats on the 35-member National Executive for grassroots representatives. At present, only six places are reserved for CLP delegates, compared with 12 for trade unionists, five for frontbenchers at Westminster, and three for MPs or MEPs. The change would give the Left, which is strongest at activist level, more influence and enable Mr Corbyn to win key votes.

Allowing CLPs, trade unions and affiliated organisations to nominate candidates in a future leadership contest, ensuring a Left-winger can stand as Mr Corbyn’s successor. It would strip MPs at Westminster of an effective veto — which twice kept John McDonnell off the ballot. Under current rules, candidates need nominations from 15 per cent of MPs and MEPs to stand.

The changes will be highly controversial with MPs but an old ally of Mr Corbyn said his election success gave him a window to stamp his mark.

“Jeremy will never be stronger than he is today,” said the friend. “We need to put our energy into changing the leadership rules.”

Critics of Mr Corbyn fear his supporters are planning even more radical changes, including making it easier for activists to deselect a sitting MP. However, sources close to the leader said they did not recognise this plan.

A source said: “Jeremy has a genuine view that he wants Labour to be a more democratic and participatory party. He always aligns himself with the grassroots and he believes that more engagement and participation was a key to our success in the general election.”

Supporters of Mr Corbyn rounded on yesterday’s Euro-rebels for indulging in the “worst kind of gesture politics”. But ringleader Chuka Umunna, the former shadow business secretary, vowed to carry on campaigning with pro-European MPs from other parties to prevent a “hard Brexit”.

Forty-nine Labour MPs voted for Mr Umunna’s amendment calling for the UK to stay in the European single market and customs union, while a 50th rebelled by acting as a teller. Labour frontbencher Ruth Cadbury, who supported the amendment, said she knew she would have to be sacked but the issue was too important for “jobs, trade and certainty for business”.

Union boss Dave Prentis condemned the rebels, saying: “Undoubtedly Europe is and will remain an important issue, but when unity is so important in the Labour Party it is utterly self-defeating to become bogged down in the worst kind of gesture politics.”

Liberal Democrat leader Tim Farron said: “Millions of people who voted for Jeremy Corbyn were hoping for a new approach to Brexit. They will be feeling utterly betrayed.”@JoeMurphyLondon