City buses operating around Iraklio, Rethymno and Hania service mostly the residential suburbs and thus are rarely useful for visitors. Tickets are normally bought at periptera (kiosks) or from the driver.
Taxis are widely available except in remote villages, and are relatively cheap by European standards. Large towns have taxi stands that post a list of prices to outlying destinations, which removes anxiety about overcharging. Otherwise, in cities make sure the meter is used. Rural taxis often do not have meters, so you should always settle on a price before getting in.
The trip from London to Iraklio by air generates 0.55 metric tons of emission. If you’re driving, it’s about the same or more, depending on your vehicle. However, travelling by train, you can cut that number down dramatically to just 0.05 metric tons.
Of course, travelling to Crete by train is not quick. Depending on where you started, budget two or three days. Coming from London would see you catching the Eurostar to Paris and then a train to Milan in Italy. From there, a coastal train takes you to Bari where there’s an overnight boat to Patra on the Peloponnese. Or train from Paris to Venice, then boat to Patra. From Patra, a bus takes you to Athens’ port at Piraeus where you catch the Crete-bound ferry. See www.raileurope.com for more routes and tickets.
It’s also possible to travel by train all the way to Athens from London/Paris via Munich, Zagreb, Belgrade and Thessaloniki, or via Budapest, Sofia and Thessaloniki. The excellent website www.seat61.com has comprehensive details.