I am somewhat frustrated by all this and I am sure that I am not alone. I hold a UK-issued EASA PPL. Its validity expires on 31 March 2021 (ie end of second year).
The licence is valid for life. Presumably you mean that the expiry date of your SEP Class Rating is 31 Mar 2021?
I have not flown for a year and so consider that I need some refresher training with an instructor before my next solo flight.
Very sensible - if your Class Rating is valid. Unfortunately the current DfT guidance precludes that before 12 Apr 2021.
In normal circumstances I would have expected to have taken a proficiency check before the expiry date but as this has to be within 3 months of expiry and we have been in lockdown for the whole of this period, I have not achieved it.
There is NO such '3 month' requirement! If you choose to revalidate by Proficiency Check and do so more than 3 months before your Class Rating validity expiry date, then the new validity expiry date will be 2 years from the date of the Proficiency Check.
Moreover to start any flying with an instructor and to prepare and undertake the check will not be possible until mid April, after the expiry date. From the CAA documentation it would seem that anyone who has had an expiry date since November is in the same position.
In which case it'll be a Renewal Proficiency Check rather than a Revalidation Proficiency Check. No difference in content; however, your ATO/DTO will need to include a document stating what refresher training was deemed necessary before you took the Check. Which can in many cases be "No training required".