The yellow smudge in these pictures is a brimstone butterfly resting on a bush, right at the limit of my lens’s zoom ability. It’s a male: the females are paler. A few minutes later one was seen fluttering in the distance, likely the same individual.
Most of the bluebells along the Railway Walk are not showing signs of flowering for a little while yet. But one small patch where the path goes through a cutting is ahead of the rest.