When did the RAF start using I.F.F. on its A/C

Once again I need some help. I am starting on a 1/48 Spitfire MK 1A. The drawings show two wires running from the Fuselage to the tips of the horizontal stabilizers. It is my understanding that these were for an IFF Xmitter. Did the RAF use IFF during the Battle of Britain?

Thanks
John