Following a report of mines of this micro being found in Newport, I have now found them in central Cardiff. They can be a lot more subtle than the pictures on the ukleafminers website!
Here is a photo showing how tricky to spot they are:
From a distance all you can see is a feint dark grey line. Up close, you can then see the egg at the left end of the mine. I also found keys that just had eggs and no obvious mine at all. Unlike the miner on Field Maple, you really need to look closely at the keys!
Another few photos from this morning in Llanishen:
Here is the egg with no sign of the mine at all.
Then on the other side is the exit hole.
Finally, on the wing is the cocoon.