[MrJohz]

The time format in the UK is mostly 12hr, although people are generally aware of 24hr time. In my experience, while there are usually more similarities between the UK and the rest of Europe, Europeans also have more exposure to American English than to British English, so it ends up being a bit of a wash, particularly when it comes to pronunciation, spelling, or idioms.

[Symbiote]

In the UK anything "serious" like a train/plane ticket/timetable uses the 24 hour clock. That includes the default way to show a digital clock on a watch, phone or computer.

[MrJohz]

Timetables yes, but whenever I've bought a digital watch or set up a new device, the default has always been 12-hour. If you ask people the time in the afternoon, they will almost always give you the 12-hour format. People can understand both, but typically default to 12-hour times.

This is in stark constrast to Germany, say, where people colloquially use 24-hour times, with some exceptions for round times (e.g. 17:00 might be called "um fünf", but 17:05 would usually be described as "siebzehn uhr fünf", roughly translated as "seventeen oh five".

This might have changed in the last five years or so since I was living in the UK, but I've never noticed this be different when I was visiting, nor when speaking to British friends or colleagues.

[carlosjobim]

Not "serious" per se, but anything which can be subject to misunderstanding.

[hdgvhicv]

It’s been years since I saw any am/pm time in written form, while people will say 7:30, they will write 19:30

[roryirvine]

In my experience, people do sometimes still use am/pm for whole hour times ("4pm"), especially in informal writing.

But it would be beyond bizarre to write "3:59 pm"

[abanana]

"Beyond bizarre"? Why? "3:59pm" (and 7:30pm, regarding the post above) is exactly what's usually written in the UK. Technical use (24-hour) is different from the standard use used by the general population.