Massive bird of prey (Sorry - didn't get a pic)

I'm less convinced now. That buzzard looks a lot like what we saw. But then so did the hen harrier.

 

If it was Massive then you are talking Golden Eagle etc and if it was a red/brown colour it might have been a Harris Hawk,but was probably a Buzzard,adult or Immature.

I doubt if it was a Sparrowhawk as you said Massive although they do like to sit on fence posts etc but would be the wrong colour so Red Kite or the Harris Hawk might be a better bet...