Easy trip. Check out seat61’s website if you don’t know it yet.

You can do it by interrail or if Sicily is your only option also looking into single tickets might be an option to compare the prices (due to the reservations fees which might sum up for interrail).

You could do London->Paris->Zürich->Milano and from there the direct nighttrain to Sicily (if you use interrail cheapest to use TGV only until Mulhouse and from there normal trains until Zürich, same for Zürich-Milano → change in Lugano to the RE to Milano, it will save you the reservation fee. Lugano is also great for a lunch stopover, there’s a nice restaurant at the station or you can walk the 10mins down to the lake/center and find some restaurant there)
Other option is London->Paris->Milano (direct train, some of them not included in INterrail AFAIK and reservation fees high) and nighttrain.

Also you could go from Paris to Marseille → Nice and then through Liguria to Rome (or hop somewhere on the nighttrain Milano-Sicily). From Rome there are also two daytime trains to Sicily (slow IC).
If you don’t like nighttrains, take the high speed train from Milano to Villa S. Giovanni and get the 20min ferry across to Sicily and from there continue by regional train to your destination(s). The ferry is not included in Interrail, but should be only around 2,5 euro.

Hi, I have not done this, but you can use for this the Interrail Global Pass. You have only to keep in mind that some trains needs a reservation like

Eurostar London-Paris 30€

TGV Paris-Milan 35€ (Frecciarossa service Paris-Milan not in Pass network, but some times it cost less than the TGV reservation). 

Intercitty Notte Milan-Sicily depends if couchette or sleeper car.  You can also use day time trains to South Italy and from there with the Ship or with the direct IC trains to Sicily (3€/seat for IC, Frecciarossa 10€) 

The advice from the experienced travellers in the community is to use other ways to make reservations than the Interrail/Eurail website.  You can look at the guide in the link:

All sounding a little complicated, I’ll try to get my head round all this.  Wanted a day time train along the Adriatic coast rather than night.  Saw something about the train goes on the ferry to Sicily.  Hoping to have a little excitement and avoid expensive airfares plus of course our bit for the planet.  We have only travelled by train as far as Brugue so far.  Thank you all.

Sorry the adriatic Coast is on the other side of Italy (Ancona/Bari) 

But yes the Milan to Palermo/Syracusa Nighttrain goes along the Coast my Suggestion is to take the Nighttrain to Milan Northbound as you have then from Lunch to Dinner the sea view til Salerno Fall asleep and wake up in La Spezia just in time  for Cinque Terre. 

The southbound train Starts at  20.40 from Milan which means it will be already dark when you pass the Cinque Terre. 

Just Note southbound a delay of 80 to 90 mins is Common. The ferry cause sometimes quite huge delays 

tuesday the southbound train had already 180mim on the mainland

My experience Northbound almost ontime 

Better views (i had luck and this Time my cabin window Was on the sea side could enjoy the view from my bed ) 

Single sleeper Tickets can be bocked from 89.90€