Labour's General Secretary Jennie Formby has written to Labour MPs asking them if they intend to stand as candidates in the next election. She wants a reply by 8 July.

BBC political correspondent Iain Watson explains why.

The Labour NEC inner core - 'the officers' group' - met today to discuss parliamentary selections.

The fact that the party's leading official - the General Secretary Jennie Formby - is writing to MPs to find out if they intend to re-stand as Labour candidates is evidence that the opposition are putting themselves on an election footing.

This is in case a confidence vote against a new Conservative leader succeeds - or indeed if that new leader calls a general election themselves.

But that's unlikely to be the only reason for the letter.

Trigger happy

One source told me the NEC officers discussed "trigger ballots"- i.e. the process of selection/de-selection - at their meeting.

It seems they haven't changed the rules to make deselections easier - but MPs can still be ousted under existing rules.

Essentially, a local party can decide to "trigger" a contest rather than automatically re-adopt the sitting MP.

The incumbent -if s/he doesn't throw in the towel - then has to face a competition to become the Labour election candidate.

Some on the Left wanted to see "open" selections in all cases, but that failed to get the support of big unions at last year's Labour conference.

But irrespective of the formal process of selection/reselection, if a snap election is called, the sitting MP is - basically - automatically reselected.

And the Left felt they were lumbered with some MPs they didn't want, but couldn't get rid of, in 2017.

So the Formby letter could be the first step in the process of finding out where battles - should the Left want to fight them - would or wouldn't be necessary.

I.e. if an MP they don't like says they intend to go, there would be no need for a trigger ballot and a row in that constituency.

Changing the party

Jeremy Corbyn has drawn his authority from Labour's wider membership, not its MPs. The recent meeting of the Parliamentary Labour Party (PLP) which he addressed in the wake of the European elections was particularly fractious.

So by firing the starting gun on the parliamentary selection process today, local parties would have time to change candidates before an autumn poll.

This could be the start of a process which reshapes the PLP a bit more in the image of the leadership - though in practice the changes may not be all that dramatic.

Some MPs may be judged more on work rate, or indeed on Brexit, rather than purely on where they stand in a left/right spectrum.

But by smoking out the intentions of sitting MPs, the party's factions will better know where they needs to focus their efforts if they want to change the personnel and politics of the PLP.