Eurasian Crag Martin, Church of St Mary and All Saints, Chesterfield. What time is it?

I'VE NEVER BEEN TO CHESTERFIELD. I only saw it on football results before. It's not the kind of place you go to for any other reason. It's not on the way to anywhere but it is now on the UK's birding map! Rocket and I dragged ourselves there this afternoon to see the Eurasian Crag Martin, which has taken up temporary residence at the crooked spired church of St Mary and All Saints in the town centre. What odds on predicting this one? Another event in our ornithological history!