Witness Account

I was driving past Swindon UK at about 6 pm . Not much traffic. As I approached a bridge I looked up and could see a huge ( about 500 ft) long diamond/ triangular craft crossing very slowly before me. I wound my window down. There was no sound. My radio was working ok. The craft past me and then turned at right angles to me. Underneath it was covered in pipes and all kinds of small colored lights. I was driving near a RAF base so I thought maybe this was a black project craft. But then as it passed over a field it shone a purple light down and the sheep starting running around in panic. I briefly looked back to see where I was driving. When I looked back the craft was gone!