Opinion: Why both Labour and the Tories should be having jangling nerves, says Chris Moncrieff.

Will they never learn? You would have thought that by now the Labour Party would have been aware of the perils of public and internal squabbling during a general election campaign.

Yet here we have Nia Griffith, the shadow defence secretary, having a very public blast with Emily Thornberry, the shadow foreign secretary, over the key issue of Trident.

It does not - believe it or not - appear to have entered their heads that a political party, whose members fight among each other rather than reserving their energies for their real opponents, is a real turn-off for voters who want the party of their choice at least to be at peace with itself.

There will be plenty of time and excuses for Labour Party blood-letting after the election if the party finds itself still in opposition.

Indeed there is even talk already among some resigned members of the party's rank and file of setting up a breakaway party if this happens, in the style of the old and ill-fated SDP in the early 1980s.

Such pessimistic talk (even if justified) is no way to conduct a general election campaign - it almost invites defeat.

But for many Labour MPs, the prospect of another five years in opposition, especially under Jeremy Corbyn, is more than they can bear.

There is bound to be a leadership election in the event of a Labour defeat, but unless Corbyn quits voluntarily, he may be more difficult to shift than is generally realised

So, stormy days ahead for Labour. Indeed, there will still be huge problems for Corbyn even if Labour win. So take cover!

And there must have been some jangling nerves among the Conservative leadership at the weekend when Labour considerably reduced their deficit in the opinion polls. This has almost certainly come about because of the Conservative proposal to make more old people pay for care.

Despite this setback, the Tories said they had no plans to amend this policy - but yesterday they had to refine it after claims it was a 'dementia tax'.

Politicians who upset what is known as the 'grey vote' do so at their peril. It is the older people, more than any other section of the electorate, who turn out to vote in the biggest numbers on polling day. So this was a gamble by Theresa May.

But this is almost certainly the reason why the Tories have stepped up their attack on Corbyn, warning that the tough Brussels grandees would make mincemeat of him if he led Britain's Brexit negotiations.

This has given Corbyn a new line of attack on the Tories which, to his credit, he has successfully exploited.