Yes - there is a shortage, more so in the future, but at the moment training is limited and quite expensive. Despite your military experience you are still an 'unknown entity' and as such, especially in the current financial climate (approx £50K including accomodation, if you can get a course place outside NATS), you're too much of a risk. (not all military controllers have managed to cross over succesfully, and that's a known fact which they will no doubt be considering). Lots of places prefer to train their own assistants and nurture from within the organisation
If you really wanted to get a UK licence then the only option may be to pay for your own ADC course and then throw yourself at the market - a
huge risk and with no guarantee of a job at the end of it. At least then you'll have shown willing and you might get sponsorship for APP and APR (but beware - APP is where a few military controllers have problems, having not done similar in the military).
As to the ICAO licence. No, it's not recognised here and probably won't be for the forseeable future. For a start some of the ICAO procedural separation standards are different to the UK. That's just one difference, there are others. Licenses are being harmonised throughout Europe but only in terms of the ratings and endorsements meaning the same. What it will do though is give you the chance to work in areas such as the middle east (if you ever wanted to - there's an expat community there), or Europe, or may even get you across into NavCanada should you fulfill the residency requirements after a stint in coldest Labrador (I take it that's where the job would be
)
Sorry to be doom and despondency - but it's a harsh world out there where ATC, although necessary, is seen more and more as a drain on finances without producing anything visible. (We know we do - safety - but try telling airport management that
)