Southwark Council are running a session tomorrow (25th) 2-6pm at Camberwell Green, see here. If this doesn't suit, might be worth speaking to them (contact details on website) about other events following this.
thanks - got there early - had my service - and they threw in some dinky free LEDs
they straightened the wheels and adjusted the gears and brakes - feels like a new bike
next one isnt till sept i think
(its to promote winter cycling)