Just to be contrary I don't think it's either of those Hard to tell though sorry. Have a look at the comparison photos on this page and you can work it out based on the pattern of black stripes on the side of the thorax. https://british-dragonflies.org.uk/species/azure-damselfly/ Too many stripes for the common blue by the looks of it and the tail isn't black enough for the blue-tailed.
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In the sticks near Peterborough
https://british-dragonflies.org.uk/odonata/damselflies/
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.