Short version: If you're a science fiction/fantasy writer who got an invitation to speak from Bexley College in the UK, someone's trying to scam you.
Longer version:
Here's an e-mail in my box today:
Greetings John Scalzi,
I am Prof. Arthur Peterson from Bexley College (Holly Hill Campus) here in London UK. We are officially writing to invite you and confirm your booking as our guest Speaker at this Year Bexley college Seminar which will take place here at the campus ground.
A scam warning from Scalzi. This one seems to be targeting SF/F writers, but I imagine similar schemes exist for other genres, as well. I don't always go to conventions, but when I do they're legit cons run by good folks. Stay wary, my friends.

I’m thinking this is perfect for guys like me: has published exactly two things (jack, and shit), unknown, questionable ability… I show up, gain instant street cred, say some words about writing, and viola: immawriter!
I don’t think the scammers are being selective. It’s not as though Scalzi’s a n00b or anything.
Soooo….
Maybe I shouldn’t be packing for my flight to London (which was inexplicably, and one hopes temporarily, to Kent for this event)?
I hope the Nigerian prince is okay. I lost track of him after his plans fell through. If things has worked out, he’d be free and I’d have enough money to take my family and friends to hear me speak at Bexley College. (I was thinking maybe I could stay on as an English teacher; it’s clear they need help with composition.)
Enjoy your flight!