London and Italy

Does the ten days include the flying days ? I would stick to one country. Perhaps Milan, Venice, Florence for ten days since most of your cities listed are in Italy. Capri is too far away. At this point , I'd recommend you get the RS Guide books for these countries, and do more research. The books include suggested itineraries. I'd also recommend you watch the RS shows/videos, review Trip Reports here, and also read the posts here under Italy and England. There's a wealth of posted info. Your questions are too broad at this point. We don't know your interests , travel styles, budget, etc.
You have lots of time to plan. Enjoy your research, and come back with more targeted questions. Safe Travels!

I would do London and Florence/Tuscany. 5 days for each.

With 10 days, I agree with Pat that 3 locations would be a good start - hopefully that is 10 days in country.

Staying within Italy is one option. Another might be to fly into London for 4 days, then fly to Milan and divide your remaining time there (maybe Milan and Florence). If you choose 2 countries, definitely book multi-city airfare: i.e. into London and home from Milan, or some variation that works with the cities you choose. You can probably find a fairly inexpensive flight London to Milan or Florence (or maybe even Pisa). Google flights will help you as you search.

That’s a short time for flying international. Even a few more days would make some difference.

If you need to keep it to 10 days inside Europe, I would fly into Venice (love Venice!) for four nights with a day-trip train over to Verona on one of those days. Take the train to Florence for four nights & have some mini-van type day tours to Tuscany, and/or take a train over to Pisa + Lucca. Then take the train to Milan for your last two nights. For this itinerary purchase a “multi-city” ticket where you fly into one city and leave from a different city - all on one reservation ticket.

If you can add a few more days, start in London with four nights, drop Venice & Florence to three nights. Fly into London and home from Milan. Buy an extra flight separately for the London-to-Venice on a carrier, such as Easy Jet.

Your arrival day and the next day will have some jet lag, so trying to do just two night in London wouldn’t be nearly as fun.

Thank you all so much!! Very helpful

Five of the six places you listed are in Italy. That being the case, I suspect Italy is calling you a lot louder than London. Suggest flying in to Venice. It is a great place to recover from jet lag, and is also one of the most unique places ever. Split your time between there and Florence and you can do day trips from each. Fly home from Florence or perhaps Milan. Remember, every time you change locations, you'll lose one half to three quarters of a day just moving. Let us know what you decide, and we'll be able to offer more specific info.

For me, personally, I'd fly into Milan. I would suggest 2 days in Milan and then hop the train to Venice. Two or three days in Venice is enough for a decent first visit. Then I'd fly to London for the last 4-5 days before flying home from LHR. It's not that I prefer London more, it's just that London is huge and seeing a couple of sites can take up an entire day. Venice is so compact which makes seeing nearly everything possible in 2-3 days. I have done this itinerary before and it was a lot of fun. Whatever you decide will be fine, just don't try to squeeze in too much. More time in fewer places is always better, to me, that less time in many places.