Been getting rather envious of all these nice migrant being posted here but last night I caught my own.
Found it on the sheet late last night and immediately knew it was a migrant, not sure why, but I could tell. A quick look through the book and found Antigastra catalaunalis. Sure enough Peter later confirmed this tiny micro migrant, which had probably come from Southern Europe/Tropics.
It's described as "a very scarce migrant, occurring only in the southern counties". It's also a new county record.