I simply don't believe Labour is as stupid as this suggests, though that has usually been a more than an adequate explanation for its past errors. This must be deliberate policy.
It is terrible to believe that fellow citizens of any political stripe would drive the British economy further into the mire for political gain, but we can't ignore the fact that it positions Labour perfectly for its favourite stance in opposition; screaming witlessly about "Tory cuts!" The very cuts that Labour has repeatedly forced on its successors by managing the national finances like an optimistic drunk.
British politics for the last 60 years has been the story of the Labour Party. It has set the agenda in all key respects. If the Conservatives are ever to be more than the guy in Pulp Fiction brought in to clear up after a messy "hit", they have somehow to take the initiative. Cameron doesn't look like the man for that job.