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Trade unions and left-wing groups are set to be given formal roles helping to run the Jeremy Corbyn-supporting campaign body Momentum.

Activists have been told that unions and "established left organisations" will get a place in its structure.

Momentum - the successor body to Mr Corbyn's Labour Party leadership campaign - has revealed almost nothing about how it is run.

But leaks to the BBC show an outline arrangement has been agreed.

One Momentum source said it may consider affiliating to the Labour Party - a move that could give it a direct say in policy decisions and, potentially, the de-selection of MPs.

Critical Labour MPs fear Momentum could let hard-left activists influence Labour and oust sitting MPs.

Momentum says it is a mass movement for progressive politics.

Jon Lansman - a key figure in Mr Corbyn's leadership bid and in Momentum - is understood to have told activists that trade unions will be involved at a "local, regional and national level".

Sources said the final structure of the organisation was yet to be confirmed.