Hello BAP
You mentioned revalidating your SEP rating as a first step - why not contact Flintshire Flying School at Hawarden? They can go over your current hours and licences and advise you how to proceed. Do you have an original CAA PPL or do you have an EASA licence to which SEP could be added?
As you surmised, a few sorties for "de-rusting" followed by a Skill Test should get you legal then you can look for somewhere to continue flying...