The excellent IanVisits website has an intriguing report that double-decker trains are being considered as a longer-term option for peak Southwestern services between Waterloo and Basingstoke, and possibly Southampton.

Double-decker trains are widely used in Europe for suburban services.  There are also double-decker high-speed trains in France. Our photo shows a double-decker commuter train operated by SNCF in Paris – and SNCF ultimately own 25% of Southeastern (through Keolis).

Introducing them in Britain is difficult because, while we have the same 4ft 8½in track, the tunnels and bridges the Victorians built have a smaller  and lower “loading  gauge“. This means that useful double-decker trains would not fit. Changing this would be a massive and disruptive infrastructure project. So there’s no prospect of double-decker trains reaching Sevenoaks.

Interestingly the constraints should not apply to services operating only on the HS1 line between Ashford and St Pancras. That line has been built to the standard European UIC gauge, as will HS2. Some of the HS1 domestic trains are already over-crowded, only 6 years after the line opened. However the loading gauge constraints would mean that double-decker trains could not go beyond Ashford to Dover and Deal without major investment (although perhaps something could be done on the largely flat Marshlink line to Hastings? – a thought for our friends at the St Leonards and Hastings Rail Improvement Programme).

IanVisits has also found a fascinating video of the prototype double-decker trains used between Dartford and London from 1949 to 1971 – which the newly-formed Dartford Rail Travellers Association will no doubt be studying carefully for its initial meeting tomorrow evening.