Growing in the garden pond, with Marsh Marigold and Flag, probably introduced.
No interactions present.
How big are the flowers?
Flowers similar size to Changing Forget-me-not, can't reach them to measure accurately.
... then Myosotis laxa seems at first sight the best bet.
I'll look that one up in Rose
Lat/Lng: 52.4418, -0.2838
OS grid ref: TL167840