I got a message saying my iCloud Id has expired. The text has a link and wants me to enter bank details. Is this dodgy

Don't reply or respond! Sounds like a phishing attempt.

http://www.apple.com/legal/more-resources/phishing/

Identifying fraudulent "phishing" email - Apple Support

Its a scam, do not provide any information at all.

iCloud accounts never expire.

And Apple will never require bank details on a website.

If you provided any passwords, change them immediately.