I was able to shoot a few images of this rather confused dance around the sky.
It appeared that two male Brimstone butterflies were chasing after a female Small White. I think they had confused the Small White with a female Brimstone which is a paler colour of the male Brimstone. Having said that the Small White is quite a bit smaller than the Brimstone.
Anyway, one of the Brimstones gave up after a while and shortly after that, so did the other and then I was able to take this shot of the Small White below.
Heard my first Nightingale and Willow Warbler of the year yesterday and also observed first Blackcap (male) of the year whilst walking along a track in the Woodland that I walk regularly.