This was a provision under the old JAA provided by the U.K. CAA Authority. The license was restricted to "G" registered aircraft. You didn't receive a frozen ATPL (they are issued to pilots that complete the exams but don't have the experience for the ATPL).

From my understanding this provision was done away with under EASA. Once you begin your exams you have 18 months to complete.

For Holders of an ICAO ATPL & Want to Convert to an Unrestricted EASA ATPL
If you hold a EASA Class 1 medical, R/T license, more than 1,500 hours on multi‐pilot aircraft, are type rated already, and have more than 500 hours on type: You are still required to pass all of the 14 EASA ATPL theoretical exams under the direction of an approved training organisation; however you are not required to attend a formal ground school. On completion of passing the examinations, you may complete the training as required in the simulator of which you have more than 500 hours on type, and on which an ATPL skills test will be conducted by an EASA flight ops inspector.

It took me 10.5 months 5 days a week to complete whilst working for a European Airline.