I saw one of those a couple of years ago in the garden of the B&B we stayed at when visiting the Air tattoo. Didn't have a clue what it was at the time and had to do some research to find out it was a Green Woodpecker.
They're hard as nails and the cats are dumb but not THAT dumb! The young birds spread out in the late summer and autumn looking for a territory and so you do tend to see them a lot more at that time of year. I seem to hear them more often than I see them, they have a very distinctive laughing call (known as a 'yaffle').
Something I didn't know
From the BTO website
TitBit: The tongue of the Green Woodpecker is so long (10cm) it has to be curled round its skull. The tongue, which is armed with barbs at the end is used for extracting ants.