There are 6 species of Mosaic Hawkers in the UK.
One of the more useful distinctions is the pattern on the side of the thorax IF you can see it. [If you can’t see the thorax, try these alternative features.]
I’ve tried to keep similarly marked species together. Some have restricted ranges, notably the Azure Hawker (Aeshna carulea) which is limited to western parts of Scotland. Likewise, the Southern Migrant Hawker/Blue-eyed Hawker (Aeshna affinis) has a stronghold in East Anglia but is spreading whilst the Common Hawker (Aeshna jumcea) famously isn’t, being absent from several parts of the country.