James Silverton:
To settle arguments here, can anyone tell me what are the fastest
scheduled long distance trains in Britain? Are there any other trains as
fast as the Chunnel train? How is timekeeping on the fast trains?

Graham Harrison:
The maximum permitted speed is 125mph but much track does not permit that
speed. Two train types were built (or intended) to operate faster but they
have never been permitted to achieve their higher speed.

The Eurostar trains that operate London/Paris and Brussels via the Channel
Tunnel have a maximum permitted 186 mph. Commuter trains using the same
tracks are currently being used in limited service and will operate to a
permitted maximum of 140 mph.

All of this is correct, except that "much track does not permit" is
perhaps a bit strong. There are three main lines in Britain today,
all built originally for lower speeds, that have been upgraded to
125 mph speed limits:

* East Coast Main Line, which leads north from London (King's Cross)
to York, Newcastle, and Edinburgh. I'm not sure exactly how far
north the 125 mph speed limit extends; maybe Newcastle.

* West Coast Main Line, which leads north from London (Euston) and
splits into different branches serving Liverpool, Manchester,
Birmingham, and Glasgow. Only tilting trains are allowed 125 mph
on this line, I believe from London as far as the Midlands (i.e.
Birmingham, Manchester, etc.) and some sections on the Glasgow route.

* Great Western Main Line, which leads west from London (Paddington)
to Reading, Bath, Bristol, and Cardiff. I believe the 125 mph
speed limit applies as far as Bristol. Trains capable of 125 mph
are used on the services to Exeter, Plymouth, and Penzance, but
only run at full speed on the short section as far as Reading.

The 186 mph route from London (St. Pancras) south to the Channel Tunnel,
now called High Speed 1, is much newer and was designed for that speed.

Other main lines generally have limits around 80-100 mph.
--
Mark Brader "Inventions reached their limit long ago,
Toronto and I see no hope for further development."
-- Julius Frontinus, 1st century A.D.

My text in this article is in the public domain.