If your ATC licence is an ICAO-recognized one, you could always take a break in the Middle East for a few years and use that to get a civil licence.
NATS doesn't recognize RAF licenses, but they do give credit for some of the experience (or have in the past) in terms of pay-point after conversion. Other ATC providers in the UK may be willing to make an offer of employment subject to completion of a civil licence course, but the likelihood of them paying for the course is slim.
DFS and Skyguide (subject to language issues) may be possibilities too.
In answer to the question posed in the subject line though.....
keep walking and/or swimming downhill until the world appears upside down and you're now going uphill.