For a great many years BT have run their own time server at time.lon.bt.com
As of today time.lon.bt.com isn't returning a DNS record, and the IP address it was apparently using (147.150.36.202) isn't responding!
http://btbusiness.custhelp.com/app/answers/detail/a_id/19074/~/how-do-i-set-the-time-and-date-by-usi... says to use this time server.
Has the DNS name changed or is there a different time server I should use? Most decent ISP's run their own time server, and the BT one was always very accurate and had a low latency to my network.