Thanks Zulu ONE & Lauderdale,
I've looked further into Sheffield since first writing and the Resettlement feedback is mixed - as Zulu ONE says, they won't pay for the course unless Sheffield are ELC registered, but provided I do it in time (ie. before I leave), the Service will pay my food/accom and some costs.
Unfortunately Sheffield haven't replied to either of my e-mails, so I'm not enthralled by their service; they're hardly biting my hand off for £3k. I'll probably rule them out for now, but if someone does have contacts at Sheffield, it'd be worth their while looking into Enhanced Learning Credit Accreditation, as overseas courses are funded. Moreover, there are a lot of people walking from the RAF with up to $4k worth of ELC to spend with the organisation willing to make the effort.
I'll have a look at Navtech now...