I've looked for Essex Skippers at Hailey Park, Llandaff North on a couple of occasions since Gareth Stamp recorded one there in 2010. Last year I tried in mid July but could only find Small Skippers. Today I had another look - the first 6 I checked were Small Skipper, but then I came across this Essex, which shows the dark underside of the antennal club nicely:
This is the upperside of the same butterfly (a male) - a bit grotty to say the least:
But I did also track down a fresher one (a female):
The final result was Small 7: Essex 2.