I have no idea why this has suddenly happened, but the threat of lightning strike (warning from the new device) prompted my beloved to nip into the office and abruptly disconnect all three modems from the wall sockets, without turning the modems off first. My wife is accustomed to switch the modems off first every time before pulling cables out of the wallsockets, in case last gasp / dying gasp or whatever should prove beneficial - although our leader, Kitz, suggests that BT ignore last gasp. But anyway on this one occasion, Janet pulled the cables straight out, which might be considered a bad thing, the result though was that all three modems were above 2272 d/s sync rate, indeed one was in the ~2400 range.
Andrews and Arnold list them all as 2.27 d/s band (which presumably means roughly ATM bit rate), which has never ever happened before. Can only hope to goodness that this is sustained, I will have to offer a libation to the gods, as this is after all St Andrew's Day.