Take helicopters as an example. A field commander says 'we need ten more attack helicopters'. The MOD says 'certainly, you can have them, but there aren't any more in service, so we'll have to place an order. The acquisition and construction/testing process will take six years, shall we go ahead?"
As a result, a Prime Minister may quite truthfully say 'I didn't refuse the request'.
I suspect that this scenario has played out on several occasions recently.It isn't only politicians who can be disingenuous.