London to Paris is fastest by train, but it’s often cheaper to fly.  Try www.eurostar.com to see if you can find a cheap youth leisure fare on the Eurostar train.  Youth fares are available if you’re 25 or under.

Paris to Florence is a long, but doable train ride.  I’d look for a cheap flight first.  An overnight train is a good option if you can’t find a cheap flight.  This is a safe option if you keep your head about you and take standard precautions — the most important of which is to stay sober.

Florence back to Manchester, I’d definitely look for a flight.  Check nearby towns that you can easily reach by train for both ends if you can’t find a cheap flight for those specific cities.

Use.www.whichbudget.com to see which low cost airlines fly which routes.  Also look for tips on the cheap flights forum.

If you do fly from Paris, I’d suggest EasyJet from Paris Orly to Pisa. Then it’s a relatively brief train or bus ride to Florence. 

Thank you guys so much for the info!

Briana

Thank you!

It’s probably too late for you, but for others reading, think about an “open jaws” flight, which might allow you to arrive in Manchester, for example, but to fly home from Italy—- it saves time and money that you’d otherwise spend going back to your arrival airport. Booking these flights can easily be done on the internet—- the main idea is that your “home” airport in the US must be used for your departure and arrival home.
Also, since you’ll have time, consider the idea of taking the train from Paris to Florence, but making stops along the way. There are some very worth-while places to see, including Dijon and Beaune, Lyon, Orange, Arles, Aix-en-Provence, etc., which are either directly on your route or might require a short detour. I hope you’ll make time for a couple of places!