The threat was made at a rally at the House of Commons in London

Left-wing supporters of Labour leader Jeremy Corbyn have vowed to 'neuter' moderate MPs such as potential party leader Chuka Umunna, pictured

Left-wing supporters of Jeremy Corbyn have vowed to ‘neuter’ his moderate Labour opponents, including potential party leader Chuka Umunna, The Mail on Sunday has learned.

The threat was made last week at a rally attended by Mr Corbyn’s Shadow Chancellor John McDonnell, during which activists were urged to move against ‘Right-wing’ Labour MPs.

The demand from the hard-Left Momentum group will increase fears among Labour’s moderate wing that Mr Corbyn is planning to cement his hold over the party with a further purge of rivals.

The rally was addressed by trade union activist Hugo Pierre, who stood unsuccessfully at the last General Election on a Socialist ticket against former Labour Minister Jim Fitzpatrick in London’s Poplar and Limehouse constituency.

Mr Pierre called for voters with ‘socialist ideas in their heart’ to ‘split apart the Tories and bring Mr Corbyn to power on a socialist programme’.

Mr Pierre then told the gathering: ‘Momentum has to…make sure it keeps quiet or it neuters those people, and I have to mention names, Chuka Umunna, and other Right-wing Labour MPs who want to tie Jeremy Corbyn’s hands.’

Mr Umunna, the former Shadow Business Secretary, initially stood against Mr Corbyn in the Labour leadership battle last year, but withdrew after complaining about the level of media scrutiny.

He quit the Opposition frontbench when Mr Corbyn was elected last September and has publicly questioned whether the party can ever win power under his leadership.

Many moderates believe Mr Umunna should stand again as he is the party’s best chance of defeating the Tories.

The threat against Mr Umunna came at a rally held on Monday in the Attlee Room at the House of Commons – named after the Labour Prime Minister who created the NHS and who nationalised one-fifth of the British economy in the 1940s.

Mr McDonnell, who arrived shortly after Mr Pierre made his remarks, told the rally that ‘from a selfish point of view’.

Momentum gave him and Mr Corbyn a feeling of ‘solidarity’ as they faced ‘an onslaught from the whole establishment’.

He said ‘trying to build a social movement’ was 'as important' as winning elections.

MPs belonging to the Blairite and Brownite rumps of the party fear that more moderates could be ousted during the coming shake-up of constituency boundaries.

Activist Hugo Pierre, pictured, named Umunna as a 'right-wing' MP who wants to 'tie Corbyn's hands'

Mr Umunna’s office declined to comment but a senior Labour source said: ‘This is the problem with Momentum.

'Neutering Labour Party members does not sound like the kinder, gentler politics we were promised. Instead this all seems rather nasty and sinister.’

The disclosure came as Mr Corbyn yesterday angered Labour supporters of the Trident nuclear defence system by joining leaders of the Scottish National Party and Plaid Cymru in addressing a Campaign for Nuclear Disarmament rally in London.