AFAIK there is open skies between the UK and Turkey, or at least there are few restrictions. Airlines including Easyjet have added many new UK-Turkey scheduled flights in recent years
As for that new EU-Turkey agreement, the way I read is that Easyjet for example could operate between Germany and Turkey so long as the Germany-Turkey bilateral is either open skies or has spare frequencies. Same for Air Berlin if they wanted to fly UK-Turkey for example