Two years ago, the UK parliament rejected a plan for air strikes on Syria, a decision accepted by the prime minister with good grace. Two months ago the new business secretary, Sajid Javid, appeared to speak for the government when he tartly dismissed calls by former members of the top brass for “boots on the ground” to try to halt the advance of Islamic State, saying it was up to the people in the region to fight their own wars.

Two weeks ago David Cameron mooted UK participation in allied air strikes over Syria for the same purpose, but promised to place any proposal before parliament in the autumn. It looked as though MPs, indeed the whole of the political class, could leave Westminster with a reasonable idea of where policy stood.

No longer. A week ago it transpired, thanks to a freedom of information request lodged by human rights charity Reprieve, that British pilots had already taken part in air strikes over Syria. Ministers and their spokespeople ducked and weaved as they admitted that RAF personnel had launched air attacks, but that their actions did not really count, because: one, there were very few of them (pilots and strikes); two, the parliamentary vote two years ago concerned a different enemy (President Assad); and three, the pilots were “embedded” with US and other allied forces, and not flying British planes.

To their credit, nobody looked particularly comfortable saying any of this: there was a sense of red faces and squirming in seats. But now, even what was left of official clarity after the “embedding” admission is no more. Just days before parliament rises for the summer recess, the government has opened a new front, all rhetorical guns blazing. In fact, as presented by Cameron in his anti-radicalisation speech and by the home secretary, Theresa May, on the BBC Radio 4 Today programme, it is a double front.

Britain suddenly finds itself on the brink of at least an air war across Syria and Iraq, and another war at home against returning jihadis and Muslim extremists of every hue. Oh yes, and observe how British ministers now use the scarier American name, Isil, rather than Isis or Islamic State (which the BBC was rebuked for using).

So what exactly has changed, that the government has decided to go on to a “full spectrum” (its term) war footing just before the holiday? Partly it seems to reflect the assessment of the security services. It was they who advised that the Foreign and Commonwealth Office should ban all travel to Tunisia, even though French and German tourists are still basking on their sun loungers.

In the past, UK officials have taken what might be described as a more robust attitude towards threats and even attacks abroad, with mantras about “not giving in to terrorists”. This time, there is a travel ban, and it was introduced not in immediate response to the killing of Britons in Sousse, but a couple of weeks afterwards in the belief that such an attack could recur. Neither the weight, nor the genesis, of this reasoning was produced – nor can that be expected. Raw intelligence, as we learned from the advice on Iraq’s weapons of mass destruction, can be divulged; but it has to be interpreted by those who know about it.

In addition, retired members of the top brass have been warning for some time of the threat posed by Isis to civilisation as we know it. There was a flurry before the election, and recently the calls have multiplied. The latest eminences arguing for action are Lord Dannatt, former head of the army, and Lord Richards, former chief of the defence staff. Lord Richards was out and about last week, using every platform at his disposal to sound the alarm, and calling for a national mobilisation akin to that for the second world war.

It may not be known how far these retired service chiefs are speaking on their own account and how far as proxies for their successors – who are expected to observe the convention of quietly following their political masters – but alarms are certainly being sounded.

There has also been talk of Isis as “an existential threat”, a term picked up by Cameron (then dropped) after the attack in Tunisia. The former chiefs have also complained of a lack of political leadership in convincing the British public of the seriousness of the threat.

Maybe it was in response to this barrage that we were treated to the Cameron-May double act, which cited the urgent need to combat the threat from Isis with “British values” and effectively put the country on alert against militant Islam in our midst. Can anyone really complain of a lack of political leadership now?

So there are three elements: an assessment from the security services in the aftermath of Sousse; the crescendo of warnings from former top brass; and the activities of religious extremists, tracked or not by the security services, at home. And each is seen as one aspect of the greater threat.

What if the service chiefs are, consciously or not, making their pitch before the imminent security and defence review?

But what if the elements are more dispersed? What direct – still less existential – threat is really posed to the UK, or even Europe, by pre-medieval forces sweeping across an already fractured northern Iraq and Syria?

What if the attacker in Tunisia had little or nothing to do with Isis, beyond boastful identification with an infamous brand? What if the service chiefs are, consciously or not, making their pitch before the government’s imminent security and defence review? And if a tiny fraction of British-born Muslims set off, for whatever reason, to join Isis, how does this automatically make that barbarian force an immediate threat to our nation? The unfortunate truth is that there is no need to spend time training in Syria or Somalia if your objective is to kill some of your fellow Britons.

This is not to deny that there are threats to the UK in general, and threats from militant Islam in particular. But wrapping so many separate dangers into one big danger will not necessarily have the desired result. The public response risks being a cross between defeatism, on the grounds that nothing can be done, and scepticism, because the alarm seems out of proportion to any threat that is observed.

Even 12 years after the Iraq invasion, any British government will face difficulty convincing people of the need for a foreign war, because the well of trust remains poisoned. Official confusion and exaggeration over Isis stands to make that task harder still.