From now until the general election in May, David Cameron has few if any foreign travel plans. Following his visit to Barack Obama in the White House a month ago, the stay-at-home prime minister intends to maximise his time electioneering in this country, making only the briefest of brief foreign forays to essential European summits. What Mr Cameron seems to be running is not so much a front-porch campaign – the American tactic of staying at home and waiting for supporters to come cap in hand – as a back-yard campaign, in which he ostentatiously busies himself with local bread-and-butter issues in a venue near you, rather than bothering himself with larger global questions.

In general election year, this has an obvious logic. But it embodies something very disturbing – Mr Cameron’s willingness to pretend drawbridges can be pulled up against the world. This pretence – not the same thing as the delusion that Britain could or should solve the world’s problems – has been marked in the Ukraine crisis and in the Greek debt row, on which eurozone ministers were locked in talks on Friday. Two weeks ago Sir Richard Shirreff pointedly asked: “Where is Britain?” This week the issue resurfaced in the House of Lords EU committee’s report on Russia and Ukraine, with equally quotable comments that Britain and Europe have been “sleepwalking into this crisis”, have misread the situation “catastrophically” and that the UK has not been “as active or as visible as it could have been”.

The Lords committee report is a substantial analysis of the most dangerous piece of aggression in Europe for the past 20, perhaps even the past 50, years. What it says matters, not just as a piece of analysis of the recent past but as a signpost pointing well into the future. It argues that the EU should have seen the conflict coming and that it was slow to adapt to the realities of Russian strategy. Echoing a speech this week by the former MI6 chief Sir John Sawers, which argued for dealing with “the Russia we have, not the Russia we’d like to have”, it argues that western policy-making had become overly optimistic. It chides the Foreign Office and other EU states with loss of analytical capacity on Russia, including a decline in language skills and experience on the ground, which meant that the shifts in Moscow’s policy went underestimated. The net result, as Sir John put it this week, is “a wretched outcome for Ukrainians. But it may be the least bad attainable outcome”.

The report also details a serious failure of statecraft. It reveals the absence of a strategy to counter Vladimir Putin’s Russia while avoiding starting a worse war than the one that is still taking place in eastern Ukraine. That absence of strategy is not Britain’s fault rather than the EU’s, or vice versa. But Britain’s failure is part of it and it needs redressing. If that does not happen, the dangers of further opportunism, including against the Baltics, will mount. When Mr Cameron speaks to MPs on Monday about the latest developments in Ukraine, he should be held to account for Britain’s part in the failure. He should not pass the buck to the EU. But nor should he be allowed to rattle a sabre that proved to be blunt when it mattered. This is about real engagement with allies, not twice-reheated Churchillism.

All the UK political parties must face the implications of what has happened in Ukraine. The answers are certainly not all military. They are above all political and economic. But the experience poses military questions too, here as elsewhere. Those questions apply across Nato, where member states have reduced defence spending over the past five years by an average of 20% while Russia has increased its spending by 50%. In this country, events in Ukraine challenge the credibility of the current government’s public spending plans, which imply a 36% real-terms spending cut in defence in the coming parliament on top of the 11% cut in this one. Cuts on that scale would have implications that cannot be simply dismissed.

Nato needs to discuss the options more calmly, honestly and multilaterally than has yet happened. The UK election needs to focus on such dilemmas. The argument does not lead umbilically to more defence spending of the sort that the military lobby is pressing for. There are choices within defence budgets and about defence budgets. But the choices must be made with eyes open, not minds closed.