I was in my back garden having a cigarette. i glanced upward and noticed a flashing light in the sky, thinking it was a plane or helicopter of some kind. the object moved in a straight line at an incredibly fast speed given my guessed altitude of more than 500ft, and distance of over a mile. it was travelling northwest. the light seemed far too bright to be an airplane or helicopter, it shone as if it were a star, i might've mistaken it for a shooting star had it not been flashing – the flashing came regularly in intervals of 2 flashes and a pause [flash flash (beat) flash flash (beat)]. i felt no emotional, psychological or physical effects other than the shock at seeing its speed. i lost sight of the object as it crossed the sky, obscured by a large tree in my neighbour's garden and the tall gymnasium of the school across from my garden.