I wonder if they are running "orange Leos"? Here's a post from alt.folklore.computers in 1998. Terribly impressive. I'm not sure his age estimate is necessarily accurate, though: the final incarnation of the Leo ceased to be manufactured in the latter half of the 60s, so it may be a bit younger.
From: Deryk Barker (email@example.com)
Subject: Re: Multics
Newsgroups: alt.folklore.computers, alt.os.multics
When my wife was working for Honeywell, in the 1980s, one of the
customers she had dealings with was British Telecom.
BT, at one location, had what they called the "orange Leos".
Now, for those who don't know this, the LEO was the world's first-ever
commercially-oriented machine (1951). Even more amazingly, the Lyons
Electronic Office was designed and built by the J Lyons company,
best-known as manufacturers of cakes and for their nationwide chain of
corner tea shops.
Anyway, an "orange Leo" was an ICL 2900 mainframe (they came in orange
cabinets), emulating an ICL 1900 mainframe, emulating a GEC System 4
mainframe emulating a LEO.
30+ year old executable code over 3 architecture changes....