It says something about the ambitions still lingering in Whitehall corridors that a sober report on the defence budget crisis reminds us that "the UK will never again be a member of the select club of global superpowers". Malcolm Chalmers, author of the Royal United Services Institute report Looking into the Black Hole, published today , quickly added that Britain has not been a global superpower for decades. This is not something many of our leaders – even, it seems, such a young prime minister as David Cameron – can stomach: they suffer from post-imperial hubris. Asked by MPs this summer whether Britain remained a "full spectrum" power, Cameron said it most certainly was, flatly contradicting evidence to the Commons defence committee by the heads of the navy, army and RAF.

Ministers and MPs continue to churn out the time-worn cliche that Britain "punches above its weight". Such comments amount to meaningless rhetoric if Libya, a conflict that simply involved dropping hundreds of (albeit "smart") bombs, is taken as a yardstick. Though the US took a back seat, Britain and its European partners had to rely for crucial intelligence on American aircraft and pilotless drones.

The key questions are what can Britain afford and what its role in the world should be. Military chiefs want as much as they can, of course. However, when asked about renewing the Trident nuclear missile system, now officially estimated to cost £25bn excluding the price of warheads and running costs, they distance themselves saying the decision is entirely "political", as if they had no view of their own.

"The expense is huge and the utility … non-existent in terms of military use," Tony Blair said of Trident in his memoirs, A Journey. Blair wrote that he could see clearly the force of the "common sense and practical argument" against Trident, but in the end he thought giving it up would be "too big a downgrading of our status as a nation …"

Chalmers warns that the costs of major weapons projects remained a "major source of potential instability, with particular concerns over the looming costs of Trident renewal". Labour seems to support the project because it provides jobs (a main motive, too, for its decision to go ahead with contracts to build two large aircraft carriers for the navy) and also for a "political" reason – namely, out of fear it will be accused of putting the UK at risk if it abandons Trident. At least the defence secretary, Liam Fox, sounds as though he really believes in it.

In the wake of last year's incoherent, Treasury-driven, strategy security and defence review, General Sir David Richards, chief of the defence staff, said: "We need to look several decades ahead and decide what Britain's place in the world is." He staked a claim for Britain's military leaders to play a key part in how best to define the country's national interests and its role in the world. The nation's top brass should help to determine a "grand strategy" for Britain and revitalise "strategic thought" in Whitehall.

The latest interventions from military figures make one shudder at the thought. Britain was still a first-rate military power, not like "bloody Denmark or Belgium", observed the former head of the navy, Lord "I'm just a simple sailor" West, last week. former service chiefs said Britain needed to pour billions more into defence spending if the country were to avoid "expensive and possibly catastrophic mistakes". One of the report's authors said the Falklands are a "plum ripe for the picking" by Argentina.

There are not billions of pounds available to spend, especially not on expensive projects that might look good but, ironically, are more vulnerable and less useful than special forces, spy satellites, and cyber-weapons. The trouble for the nation's flag wavers is that these are also much less visible.