The head of the Royal Air Force (RAF) has delivered a stark critique of politicians for lacking decisiveness and "making it up as they go along".

Air Chief Marshal Sir Andrew Pulford said military figures wanted "answers now", but had to deal with civilian leaders who left everything till the last moment and were obsessed with cost.

The comments, which could irritate David Cameron and Defence Secretary Philip Hammond among others, came in a speech to a conference organised by think-tank the Royal United Services Institute (RUSI).

Sir Andrew, Chief of the Air Staff, told the event in London that the RAF's core function was to look after the airspace of British territory.

"That simple answer to what we are for is why so many governments take the easy way with their air forces," he said.

"Look at how many air forces in the world simply do that... they do the non-discretionary.

"It's that further ambition that really puzzles us.

"That balance between what the politicians might want me to do and how much they want me to pay for it, and how much time and effort and resource they wish me to invest in it.

"That has always been the way, that balance between politics and the military."

Sir Andrew went on: "I am a military man, I want an answer now. The politician - 'if I could leave it a couple of days, could you wait till the end of next week, I really don't feel like making a decision just yet. I'll leave it right till the last moment, do I have to make a decision now?'

"I want that decision now... I want to know exactly what you want me to do and I want the end state...

"The politician, he's not really sure what the end state is, he doesn't really care, he's got to be seen to be doing something, 'we need to be there, I'll make that up as we go along...'

"That doesn't sit comfortably.

"I want to take enough people and enough equipment to get the job done to meet that end state, and I want the decision now.

"'Well, can you go with fewer people, because politically I want to be seen maintaining a sort of level on this...'

"And of course, the big cruncher, 'how much is all this going to cost?' I don't care about the cost. I need the resource, the people to get the job done, get the end state in the timeline...

"'Ooh, if you could do it for a couple of million less that would be great, because the Treasury are not being quite...' That tension is there.

"Of course that's in an operational time... in peacetime we are in that balance every year.

"We are trying to balance that political ambition with my military ambition, my need to explain to the politicians, if you give me X, I can do Y."

Senior military figures have repeatedly raised concerns about the impact of the coalition's spending curbs, which have seen force levels cut and equipment programmes trimmed.

An RAF spokesman said: " The comments made by the Chief of the Air Staff must not be taken out of context. His commentary was based on previous academic discussions at the conference and related to the differences between any international military leader, who has to make decisions based on tactical circumstances and political decision makers who have to take into account a far broader and more complex picture.

"It was certainly not intended as any form of critique of the current UK Government or any previous UK Government."