Mountain less than 5 hours away from London?

Climb? There isn't a mountain in the UK you can't walk up in a few hours.

Mt Snowdon is a five-hour drive from London, maybe six depending on traffic outbound. It's thirty-five hundred feet. It'd be a bus-train affair to get to the approach point.

Ben Nevis is the highest peak n the country and it's only about a thousand feet higher. I'm sure you could get to Fort William by train but have no idea what would happen next. It'd burn the most of the day, however. It'd probably take twelve hours to drive it.

Staying in England, the highest peak is in the Lake District somewhere and it's got to be under thirty-five hundred - - maybe Scarfell Pike. It's a good seven hours to get up there by car. Otherwise it's also a bus-train combo.

They're all nice little hikes/walks, but are non-events as far as climbing goes.

Staying closer to London, there's nothing close to two thousand feet.

I'd look for a better use of twenty percent of a very short visit.

The UK doesn't really do "mountains". Big hills, yes.

Snowdon, while called a mount, is a walk up and down rather than a climb. In fact, because a train runs up to nearly the summit, you only have to walk one or none direction.

kma, you give no hint in your incomplete profile where you are coming from. Are you flatlanders for whom Snowdon will seem like Everest, or are you regular climbers who wouldn't break a sweat?

First thing I thought of is the movie "The Englishman that Went up a Hill and Came Down a Mountain." Not a Hugh Grant fan, but it's a great movie.

I would not underestimate British mountains. Although not too high in absolute height above see level but they look much bigger especially Scottish ones. You need to be prepared for weather changes etc. Ben Nevis shortened more lives than one would expect considering its height.

Scotland would be best (here's why), but is too far. Snowden is nearer, but still a bit of a drive and likewise the Lake District.

You may want to take a look at the Peak District, in the centre/north of England, and the Brecon Beacons in south Wales. They are roughly 4 hours and 3 hours from London by car and both have lots of walking opportunities that can be very challenging if you want.