T61 Falkes are non-EASA aircraft and are being transferred to national C of A and National ARC (NARC). There has been a hold up in the process at the CAA.
Following a lot of work in the past by Jim Hammerton and more recently by BGA CTO Gordon MacDonald, the CAA have just issued a revised an Airworthiness Approval Notice 22705 issue 3, that allowed the first national C of A and NARC on a Slingsby T61F to be issued.
The AAN can be found at https://siteapps.ca.co.uk/aans/. On that page, type in 22705. Issue 3 is found by opening the third PDF document at the bottom of the page.
BGA Motor glider inspectors with ARC privileges can apply for NARC signatory privileges. On successful application to the BGA, the inspector receives CAA-issued AD458 approval. Owners can contact Gordon MacDonald via the BGA office for more detail if required.