Officers say they were threatened by a man with a firearm.
The injured man is under arrest and in a stable condition in hospital.
We have referred the matter to the IPCC and will support them in their investigations."
More top news
An extreme endurance athlete from Cheltenham has become the first person in history to complete the British ultra-triathlon
A selection of images from Glastonbury Festival where the music has begun and weird and wonderful things are going on
Hundreds of people have shown their anger at the EU referendum result, demanding that our borders be kept open for migrants and refugees