Answer: First, you will go from CARDIFF to either the CHANNEL TUNNEL or to DOVER, where you will take a CAR FERRY. From Cardiff to the Channel Tunnel/Dover, it is 225/235 miles (respectively) taking this route:
Take M4(E) NEWPORT, from Cardiff, across to M25(S) GATWICK at J4B.
Take M25, around London, to M20 to the CHANNEL TUNNEL and DOVER, via M26 (at J5 on M25).
Take M20 to either the CHANNEL TUNNEL car shuttle (recommended route) (to CALIS, FRANCE) at J11, or continue on M20/A20 to DOVER, where you will board a CAR FERRY to CALAIS, FRANCE (alternate route).
Take either the CHANNEL TUNNEL car shuttle (recommended route), or the CAR FERRY (alternate route) across to CALAIS, FRANCE. The CHANNEL TUNNEL high-speed car shuttle is operated by EUROTUNNEL, and the CAR FERRY in question is operated by P&O. For more info on both, see the related links below:
Once you are in FRANCE, you will be going from Calais to the MONT BLANC TUNNEL to go into ITALY.
From Calais to the Mont Blanc Tunnel, it is about 900 kilometres (560 miles) taking this route:
Take A26 REIMS, from Calais, to A5 LYON, at the exit near Troyes.
Take A5 to A31 LYON-DIJON.
Take A31 to A39 GENÈVE.
Take A39 to A40 to MILAN.
Follow A40 to the MONT BLANC TUNNEL (toll), where you will enter into ITALY.
Please note that in France, most of the autoroutes are tolled, as is the Mont Blanc Tunnel. For more info on both the autoroutes and the MONT-BLANC TUNNEL, see the related links below:
Once you are through the MONT-BLANC ROAD TUNNEL and into ITLAY, it is 225 kilometres (140 miles) taking this route:
Continue on autostrada A5 MILANO to A4 MILANO.
Take A4 to MILANO.
Also keep in mind that, like France, the autostrade of Italy are also tolled. For more info, see the related link below:
In total, it is about 1,110/1,120 driving miles (or 1,487/1,503 kilometres), not including the Channel Tunnel/Ferry