Best bet is to telephone the CAA medical section. Wednesdays or Fridays are particularly good for this because that's when the resident medical officer is there but the ladies who work at CAA medical are very helpful and clued up anyway. You need to establish who can do the test. I suspect that you can do the flight check on a SEP at your local flight school provided that you do the check with the CFI. It must, I suspect, be the CFI. The check has nothing much to do with a flight check. It's confirmation that in practical terms you can see other aircraft, ground features, airfields etc and so on sufficiently well as to be safe.
I'm basing those suppositions on a recent hearing assessment flight test that has come to my attention.
Don't go and ask them if it has to be done by an IRE in a 747. As previous writer said, suggest to them that you do it with your CFI in a SEP.
I'm sure the check is something in the order of a forty minute vision test not a renewal of SEP privileges, departure, quick GF, join and couple of circuits sort of thing.
http://www.caa.co.uk/docs/49/2014013...dardVision.pdf