Not able to register at the moment as my computer is blocking cookies. Just to say thanks to those who answered my question about uncharacteristic behaviour.
I took Fly to the vet this afternoon. He has some marks on the backs of his legs, which she said was probably an allergic reaction, but has become infected, and gave me antibiotics and piraton. Thankfully there were no other abnormal lumps or bumps and she agreed with some of your posts that it was probably just that he felt threatened having someone invade his body space who looked like an adult. I've also had a chat with my daughter about making sure her friends still act responsibly around the dogs - there were about four of them in the house at the time - all giggly teenage girls and it was probably a bit loud too.
Thanks again for your comments - trying to sort out my computer to let me register now.

Fly's mum