Hybred Swallow Martin

While fetching the cows in yesterday evening i was watching the swallows swooping down catching insects there was one slightly different it looked like a small swallow with blue back and white underneath with a short dark tail with a faint dirty white rump i have spoken to a few people and i am convinced that it is a hybred between a house martin and a swallow richard and Janet came down the farm this afternoon but i dont think they saw it but it was windy i will look again tommorrow