SO THAT’S it then. Just when Jeremy Corbyn thought things were going pretty well for Labour, he suffers the body blow that Tom Harris — who? — has had enough.

Harris was a Labour MP in Glasgow from 2001 until May, losing his seat to Scottish nationalist Stewart McDonald.

He was briefly a junior minister before being relieved of his duties by Gordon Brown and threw his hat in the ring for Scottish Labour leader in 2011, bailing out early because of a dearth of voter enthusiasm.

Harris accused Scottish Labour then of having had “no new ideas” in 12 years of devolution, of being closer to the public sector than to business and of having failed to be “a party of aspiration.”

Given such a record of loyalty to his party, it should be no surprise now that he writes on social media of “60 per cent votes for sure-fire election losers, IRA-supporting shadow chancellors and Scottish Labour unnecessarily splitting the party on issues over which it has no responsibility” and Labour agreeing to consult Stop the War over military involvement in Syria.

“So that’s it. Labour has jumped the shark. It has gone from a bit bonkers to irredeemable in the space of a single day. And I give up. That’s it for me. Giving. Up,” he declared dramatically.

Corbyn always insists that there is room for all shades of Labour opinion within the party, but he may well believe that it’s probably time for this overexcitable comrade to have a rest.

Harris notes in desperation that 60 per cent of party members voted for Corbyn, boosting party membership that had stagnated while advocates of “responsible” economic policies and “pro-business” attitudes held sway.

One reason that thousands of people flocked to Corbyn’s rallies throughout Britain during the leadership campaign was that he eschewed New Labour’s “we love the City” approach and demanded that business pay its fair share of taxation.

He clobbered corporate tax-dodging and the comprehensive failure of HM Revenue and Customs top brass to tackle offshore tax evaders, insisting that recruitment of more staff was essential to counter this criminal conduct.

The Commons public accounts committee report on HMRC inadequacy illustrates the correctness of the stance of Corbyn and shadow chancellor John McDonnell against the complacency of the “party of business” brigade.

Tony Blair’s erstwhile spinmeister Alastair Campbell has also jumped on this bandwagon, slating Corbyn for not cancelling previous commitments to address the CBI bosses’ organisation next Monday.

Labour leaders have become too adept at tickling corporate leaders’ bellies in recent years. Priorities have to change.

Working-class interests have to be placed centre-stage. Direct state investment has to play a role in modernising infrastructure, providing well-paid employment and boosting output.

Left to itself, big business refuses to invest unless government guarantees its profits. This is an unsustainable economic model.

Former New Labour Treasury minister Liam Byrne is another to bang the drum for Labour to be “the pro-enterprise party in Britain.”

But his criticism of the Labour leadership’s “People’s Quantitative Easing” approach and his antipathy to public ownership and higher spending on essential services reflect the same discredited attachment to economic orthodoxy.

One-time party leader Neil Kinnock distances himself from the critics of the Corbyn-McDonnell investment strategy, commending their alternative economic approach to that of George Osborne.

However, he ought to rethink his insistence on knowing that “the British people will not vote for unilateral disarmament” unless by this he means that Scots don’t qualify as British.

The SNP opposes replacement of Trident nuclear-armed submarines and won all but one seat in Scotland.

Kinnock should realise that old certainties no longer apply. New situations demand new approaches, which is why the Corbyn election campaign turned Labour’s world upside down. Fresh thinking is essential.