Two male Green woodpeckers menacing each other this morning in a Surrey garden in the UK.

This morning two Green woodpeckers were alternatively swaying and moving their heads from side to side one after the other in a face off, which lasted long enough for me to grab my camera from upstairs and shoot a few burst pictures at perhaps 30m. distance from an upstairs window in a Surrey garden.

Was it a male and female in a courtship ritual?
No.
A close examination of the pictures above (shown below) reveals that both are males: characterised by red moustaches -- females have black ones.  See https://www.rspb.org.uk/birds-and-wildlife/wildlife-guides/bird-a-z/green-woodpecker
This behaviour then is a sort of harmless "shadow boxing" to establish a territorial hierarchy perhaps.

Click on any picture to expand it.

This sequence has been incorporated into my illustrated talk, "The natural year in focus" detailed at http://www.peterlovetttalks.co.uk/page13.html