Penguin in Wiltshire?

Obviously not, but can anyone help identify a bird I saw but couldn't photograph yesterday? 

It did look like a small penguin. 8-10 inches high, very upright, white front like a dickey and dark, possibly black head and back. Too far away to see it's beak/bill. The nearest I could see in the Rspb guide was Auk, but I would have thought that that is almost as unlikely as a penguin in rural Wiltshire.

Thanks

  • It finally tunnelled out of Longleat! You should have seen the teeny tiny trousers he wore to disperse the earth from the tunnel onto the flower beds!! Was it a good long look at it being upright, or a quick glance. I saw a guillemot in the week and I thought that was penguinesque when it reared up exercising it's wings
  • About 20 seconds. Just turned to get the camera and it went. The fence is 7' high so it must have flown (NOT a penguin). A very upright stance, no real neck couldn't see the wings. No discernable mud fro the tunnelling.