I’m in the UK which is objectively tiny, but going from the south to the north wouldn’t be a day trip. And if you basically spend 1 day travelling up, 1 day doing whatever team guff the company wants you to do, and 1 day going back (i.e. ~24 hours), you’ve wasted MORE time than you would have commuting an hour each workday for the whole month!
Not if you go to Scotland but Newcastle, Manchester, Liverpool (to name the most common places remote workers for London companies appear to work from what I've seen) are easily done in a day trip. Prices can be hefty but compared to spending a night in the hotel it's still cheaper for the company to pay for busy times.
Try Cornwall to Newcastle by train, more like 9-10 hours :) If I still have to pick remote jobs by which ones are close to my physical location, or pick my living area based on where jobs are, I don’t feel like the promise of remote work is really being fulfilled.
If you're all remote it's probably easiest to rent office space for those days close to a train station (or between those) in London. In that case it's probably not more than 4 hours for anyone based in the UK.
Same for other European countries. If you only need office space every other week for a day you can rent it in a central location that's easy to reach by train for anyone in the country.