For your specific itinerary, I'd mix trains and flights.
London → Paris: Take the train
The high-speed Eurostar is hard to beat.
Why:
- About 2 hours 15 minutes on the train.
- City center to city center.
- No long ride out to an airport.
- You can usually arrive 60–90 minutes before departure rather than dealing with the longer airport process.
Door-to-door, it's often around 4 hours total, and it's generally less stressful than flying.
Paris → Rome: Fly
This is where flying usually wins.
Although the flight itself is only about 2 hours, your total travel time is more like:
- 45–60 minutes to the airport
- 2 hours before departure
- 2-hour flight
- 30–60 minutes to get into Rome
So you're looking at roughly 5–6 hours door-to-door.
Could you take the train? Yes—but it's typically around 11–14 hours with one or more changes. Unless you specifically enjoy scenic rail journeys, it doesn't make much sense on a 12-day vacation.
My recommendation
- 🚆 London → Paris
- ✈️ Paris → Rome
That's the combination many experienced travelers choose.
One more tip that can save you both time and money: book an open-jaw (multi-city) ticket. For example:
- Fly into London
- Travel by train to Paris
- Fly to Rome
- Fly home from Rome
That avoids spending an extra day and money returning to your arrival city.
A final travel tip: if you take an early train or flight, resist the temptation to pack a full sightseeing day on both ends. Even a smooth travel day can be tiring, and leaving some flexibility makes the trip feel much more relaxed.