We know that Jeremy Corbyn’s Labour Party is not very popular. On topics like defence, the economy, tax, immigration and Brexit it lags well behind the Conservatives.

Traditionally, when Labour is in trouble on every front, it retreats to the NHS. It’s the Opposition’s safe space, the one field in which it knows it will always dominate public opinion.

Labour created the NHS, how could it ever lose its lead on the topic?

It turns out that the answer to this question is: by being led by Jeremy Corbyn.

As Labour has declined in the polls, it has predictably opted to talk about the health service. The ‘winter crisis’ is a favoured theme, and this weekend Corbyn said: “I don’t keep talking about the NHS because it’s in Labour’s comfort zone, I talk about the National Health Service because it’s in a danger zone”.

Despite this claim, Labour no doubt think that the NHS is indeed in their comfort zone. Surprisingly, though, it isn’t anymore. A Comres poll for The Independent on Sunday found that “Theresa May and the Conservatives would do a better job than Jeremy Corbyn and Labour at managing the NHS this winter” by a margin of 12 points, 43 per cent to 31 per cent. That’s a remarkable result in what is meant to be Labour’s home territory.

The Government hasn’t made great claims or strides on the NHS since May took over (for inescapable reasons), and indeed the same poll same poll found 47 per cent support for the Red Cross’s claim that the health service is in a state of ‘humanitarian crisis’, so this isn’t necessarily a huge endorsement for the Prime Minister. Instead, it’s a crushing verdict on Corbyn and his incapable leadership.

Nor is the poll an outlier – Survation found last week that May’s trust rating on the NHS is +4 but Corbyn’s is a disastrous -21.

There’s further evidence when you look at Labour’s reputation if you don’t mention Corbyn. YouGov last week gave Labour an eight point lead on the NHS.

That disparity strikes the most fear into Labour’s remaining sensible members – it’s bad enough that under Corbyn Labour has lost its lead on what is meant to be its strongest issue, but what if the man’s unpopularity does lasting harm to the party?

He has already driven a brain drain among Labour’s advisers, with many experienced staff jumping ship since he was first elected leader. Now, with two young MPs quitting in a matter of weeks, it seems he is also degrading the abilities of the Parliamentary Labour Party.

Those losses harm Labour’s effectiveness in day to day political operations, and will take years to overcome, but the prospect of contagion from Corbyn’s reputation to the wider Labour brand would do more fundamental damage. The Conservatives will endlessly refer to “Jeremy Corbyn’s Labour Party” in the hope that it will speed that trend along.