Possible Purple Heron, Castle Pill, nr Milford

Driving past Castle Pill this afternoon at about 1530 I saw an odd-coloured large heron feeding above the causeway. I was (just) able to stop the car and watch it for a minute or so, then while I tried to move to get a better view it disappeared; very frustrating.
My overall impression was of a very odd-coloured bird, with a mixture of dirty browns and paler colours underneath. There was no black head markings like an adult Grey Heron, but both bill and legs were yellow. The neck and breast were finely streaked.
I have never seen a Purple Heron, so do not feel at all confident about the ID, so would very be very interested if anyone else gets a chance to see it.