There were several that feed off Hazel leaves including these two which are, I believe, (the mines of) Stigmella floslactella and Phyllonorycter coryli
Here are two more we saw and had identified for us:
Stigmella anomalella on a Rose leaf. The yellow grub is clearly visible in this case (an ID feature).
Stigmella assimilella on Aspen, Populus tremula leaf.
This last is the one we might have missed the host for. It was Norman who spotted the mined leaf below a large tree. This is only the fifth record for the county I think he said.
Thanks to Steph for the pictures. I was too cold / busy with my plant card to get my camera out of the bag!