"politicians decide how much they are prepared to pay"
And in 2010 they decided we could not afford fixed wing carrier aircraft for a decade and any LRMPA after having "wasted" funds on Nimrod.
We still have a large Defence Budget but unlike the case with say NHS spending, throwing money at something was deemed not to be the answer. That's the simple politics.
Post 2015 matters will not improve. Personally, I doubt we will run on Tornado once Typhoon is cleared to carry Storm Shadow. As for ditching early Tranche Typhoons, you can imagine the reaction from the Public to another waste of money. Much easier to get rid of another "old" type altogether as has often happened in the past few years.