Ian, if you go to BTO website under Birdtrack you should be able to access maps which show the progress of migrants across the country and you can check if your date coincides with an influx.
For a more local check try the Skomer island blog(which is a good read anyway) as their sightings usually coincide with ours give or take a few days.
Otherwise you'll just have to go back in May and June. What hardship!