This depends on where in the system the train is. In central London, the speeds are lower, as the train doesn't have the time to get up to speed before it has to brake for the next station. Further out, the distances, and thus the speeds, are greater.
The systemwide average speed is 20 mph. In central London, speeds stay within 30-40 mph, but on the outer parts of the Victoria line, speeds reach up to 50 mph and can on the Metropollitan line exceed 60 mph.
anywhere between 10mph to 60 mph
60 mph
pretty fast
Virgin Trains services between London Euston and Liverpool Lime Street.
89
1mph
There is no such thing as a jet train.
busses and trains
To get back to present day London you need to visit Cogg in the Clock Shop on Midland Road.
The speed is limited by the rail authority. Turns out that empty trains can't go any faster than full trains - but, empty trains can accelerate faster. A loaded coal train can go as fast as 55 miles per hour.
Chiltern Railways trains between Aylesbury and London Marylebone call at Amersham.
You can't. The London Underground and London Buses only go as far as the suburbs. You can get direct, mainline trains from all major towns in Kent to central London, including Ashford, Chatham, Margate/Ramsgate, Maidstone, Folkestone, Tunbridge Wells and Dover. The fastest trains go to London St Pancras, others go to London Charing Cross and London Bridge stations.
Passenger trains could go as fast as 80 mph, freights were normally limited to about 30.
You will have to change trains in Edinburgh