Identify unfamiliar biting fly.

I was today bitten on the hand by a fly I had never seen previously. It was a dark non-translucent black delta wing arrangement with four small square green markings size about 12 mm long with a parked wing span of about the same.

It appeared to have a fly shaped body and head, with a proboskis which it lowered onto my skin. once I realised it was biting, I blew it away, which required a fairly hard puff, and was left with a small  6mm dia wheal which disapeared in five minutes or so.

Any idea if it is UK native, or a visitor. - We are located in East Anglia.