Why is it that in the UK we seem to prefer building stations with bridges over the line and steps going up from the platforms, whereas in Belgium, Germany etc. the vast majority seem to have the line built over an underground space with steps going down from the platforms? (At smaller stations this is just a plain underpass, but at larger ones there might be more facilities such as a shopping area and toilets).
That's not to say there aren't any underpasses in the UK - Swindon springs to mind as an example - or footbridges abroad - such as Liège-Guillemins - but they seem very much the exception.
Could it have something to do with the greater prevalence of overhead electrification in Europe leading designers to prefer going underneath? Or maybe the association of underground spaces with anti-social behaviour is greater in this country?
I suspect that the choice between footbridge or subway has more to do with the lie of the land and local requirements than any national preference. In any event the stations were mostly sited long before electrification was thing.
For example Reading used only to have a subway as the station was built on an embankment and the subway was at the original ground level; it was the only way to reach the platforms away from the booking hall. It still exists as a way between the two sides of the station outside the gateline. When the station building were extended in 1989 a footbridge was built between the new booking office and the multi-story car park; it also gave access to the island platforms. The subway still existed and was still used but was now inside the gateline.
The size of the new footbridge ("Transfer deck") which was erected in the latest rebuild a decade or so ago (when the 1989 footbridge was demolished) gives some idea of the space required if the subway had been enlarged - digging out the embankment whilst still running trains over the top would have been a complicated and expensive matter quite apart from the local ground level on the town side of the station having been raised since the railway was built making the advantages of a subway somewhat moot.
Bath station is also elevated as it's placed in a loop of the Avon - it also has a subway.
On the continent, again, local conditions in many cases made the choice obvious. In Brussels the Gare du Midi is on a high brick embankment so a subway is the obvious choice. Similarly with Köln, the station is high up as the eastern end goes straight out over the Hohenzollern Bridge over the Rhine which needs clearance for the ships. In Berlin the Stadtbahn goes through the centre of the city on a
bridge (oops, corrected in edit) viaduct so platform access at the stations along it is in general through subways. Berlin Hbf is a special case as it has multiple levels of trains...! In Hamburg although the station is on an embankment as the line goes out over the Alster lake, it has footbridges between the platforms.
