Red Line Entry.
I would pay little attention to any survey carried out as their accuracy is questionable at the best of times (especially if you disagree with the findings), and anyway you can get very different survey results by a sly rewording of the question(s).
Where would I get the money from? For a start I would reduce the foreign aid budget to little more than a holding-fund. I would put aside a £1 billion fund to help any country that had been genuinely overtaken by some natural disaster with whatever humanitarian/rescue activities we might provide. Fine.
However, the idea that we should be funding myriad projects across the planet whilst imposing austerity cuts at home is unacceptable. That would release about £10 billions.
Secondly, I would wish to withdraw from the so-called "EU" at the very earliest opportunity (they're now asking for an additional £100 millions from the UK taxpayer) This would release an additional £8 billions. That's a very useful £18 billions for starters.
Of course it wouldn't all go defence, but it would release, in the short term, a substantial amount to be spent on those defence areas that have been most damaged in recent years (a renewed Maritime Patrol/ASW platform being an obvious requirement).
I would also get Mr Murdoch on my side. As Winston said "There's no such thing as public opinion. Only published opinion."