The assisted dying bill is entering the make-or-break stage.

The message from those around Kim Leadbeater is that all is calm and well. She tells me she is “not particularly worried” about 28 MPs changing their minds and overturning the previous, historic, vote at the bill’s second reading.

But the mood at the assisted dying campaign’s press conference today is different. The cheerful optimism that marked the last one has turned to a charged nervousness.

They should be nervous. There are jitters among a number of MPs I’ve spoken to who voted for the bill last time but are concerned about safeguards and timeframes.

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MPs do not have long to make up their minds – after the Easter recess the report stage of the process will begin (probably on the 25 April) and the next vote is expected around the 16 May.

It will be the crunch vote where MPs who voted for the bill in principle – to see it debated – will need to pick a side.

Last time a majority of 55 MPs voted for assisted dying, more than many had expected but not enough to make the path to law certain.

Reform’s Lee Anderson and his former colleague Rupert Lowe have both told us they will no longer be backing the bill, having supported it last time. No Labour MPs I’ve spoken to appear to have decisively changed their mind, however.

“I would hope that some colleagues would come on board that potentially voted against it last time,” Ms Leadbeater tells me.

But the sense I get is the mood may be in the other direction.

The main issue that comes up is the removal of the requirement of a High Court judge – to be replaced by a panel of experts including a senior lawyer, psychiatrist and social worker. Ms Leadbeater says the safeguards are now stronger.

There has also been criticism that some amendments, including on closing a so-called anorexia loophole, were not selected.

Naz Shah, the Labour MP for Bradford West who did not back the assisted dying bill but claims she was “very open” to voting for it, says the process has been “fundamentally flawed”.

She says: “The intention for me was, is it going to be safer? Can I vote for this bill? Ultimately the conclusion I’ve drawn is, no, it’s not safe enough.”

There is also disquiet about the deadline for the implementation of assisted dying being pushed to four years, which some fear will mean it will be politicised in an election campaign.

Ms Leadbeater says it is “more important to do this right than to do this quickly”. She believes implementation can still be achieved in two years.

And what of the toll it has taken on the MP herself? It was always remarkable that such consequential legislation to be brought via an individual MP’s private members bill.

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Ms Leadbeater, whose sister Jo Cox was murdered when she was an MP, tells me “the personal toll has been quite hard”.

She talks about the “unpleasantness and nastiness” that has been directed towards her but believes her parliamentary colleagues have come to the argument in good faith.

“I think people have got their views and they’ve got strong views”, she says. “We all have to think about how we behave in this very privileged, very responsible job.”

One thing is for sure, it’s nearly make-your-mind-up time for MPs, and what happens next will have consequences well beyond parliament.