A face-off between two of the West Park coots, while a third looked on intently. Presumably the two birds adopting a threat posture were rival males, with an interloper getting too close to the other’s mate.
The threats didn’t develop into actual contact: that can look quite nasty with coots, deploying their vicious-looking feet as well as beaks. The onlooker eventually turned round and started swimming away. The other pair lost eye contact, and headed for well-separated parts of the bank to climb on land and walk off ignoring each other.