A
practice emergency sounds a bit like being
a little pregnant, doesn't it ?
Seriously - none of this would be necessary if the UK had a proper countrywide FIS available to VFR flights like all other countries I've ever flown in. Anywhere else you can call up xxxinfo (center, radar), request FIS / Flight Following, get a squawk and are on your way. Should you then blunder into CAS (or appear to be on your merry way doing so), you'll get a call
XXXX be aware XYZ airspace is 5 miles ahead. And please don't tell me the usual 'It's too busy here', there are other places at least as busy (Southern California comes to mind), where this is not a problem at all.
121.5 should be reserved for
real emergencies - only.