This app was mentioned in 3 comments, with an average of 2.33 upvotes
Here's the android version, for anyone interested: https://play.google.com/store/apps/details?id=com.goodsam.responder
Maybe someone on iOS could post a link to that too.
I've not used the app myself, but think I will. I'm a lapsed first aider, but in an emergency in public I'd be willing to try if no one better trained is available. Should get myself unlapsed too.
EDIT - just spotted something about only using the responder app if one's First Aid certificate is still valid. Ah well. I'll get the alerter one at least (https://play.google.com/store/apps/details?id=com.goodsam.alerter)
Download the GoodSAM Responder app and register as an NHS responder -here