This was introduced as a result of much work behind the scenes by the LAA to re-introduce authorisation for CAA Revalidation Examiners to sign EASA licences following withdrawal of these privileges at the introduction of EASA in September 2012.
And I think its great that this has come into effect. I and I think many others think iot would have been even better and easier if they had been given the same priviledges at examiners