Of course there won't be any extra cash for the MOD. It will all come under the guise of 'security' which means paying for new uniforms for Customs Officers at Dover or hiring a few more pretty young things to carry out initial interviews for terrorists wanting UK passports.
However, I fully expect it to be portrayed as a significant investment in the UK's defence capability. Just like the portrayed significant reduction in the basic rate of income tax (without mentioning the effective doubling of the lowest 10% rate of tax).
Yet more spin spin spin.. Oh I'm starting to feel dizzy .... can I get off?