I was in the middle of a phone call last night, when the line went dead.

I waited 30 seconds for the other party to put the phone down and then redialed.

I then heard the three rising bleeps (as just before "the number you have dialed is unavailable"), and heard the message: "The number you have dialed is not accepting calls at the moment".

As far as I was aware there is no mechanism to set a landline to reject calls (and I've always thought it odd that I've never seen a phone with an "off" switch).

I redialed a few minutes later and was connected with no problem.

Any ideas?

You can subscribe to a number of BT services that will bar incoming calls.

Anonymous Call Reject bars all calls with the CLI withheld.
Choose To Refuse allows you to bar up to ten numbers of your choice
Call Barring can bar all incoming or outgoing calls

http://www.downloads.bt.com/callingf...S_Download_PDF

All these require a subscription however and need the subscriber to enter codes at the handset.

What is much more likely is a network or exchange problem that zapped the line temporarily.

I doubt it's a network/exchange thing.. It could be someone's implemented a subscriber facililty option to do a 'do not disturb' feature. It's not something I've heard & figuring it out would need the call signalling information, which unless you're on ISDN you'd not be able to see. Usually if it's a network problem, you'd get a variation on the 'unavailable' or a busy tone.