When I sent Form SRG 1104 to CAA last year to renew my ATPL
A JAA ATPL is deemed to be an EASA licence, so if it is current the CAA should issue an EASA licence without valid class/type ratings as it is, simplistically, a swap.
If it is a renewal, then it falls into the issue of a licence, so valid class/type rating plus medical required.
XO