Taken from the Heathrow Airport WEB Site: http://www.heathrowairport.com/plan-...ling-with-pets

Airlines

Airlines will only carry animals if advanced arrangements have been made, as space is often limited. There are two options and your airline will be able to tell you which services they are able to offer:

Accompanied baggage – most airlines will accept animals as accompanied baggage providing they are in a suitable container. They will travel in the baggage compartment where a suitable environment can be maintained (note – animals arriving in the UK may only do so as manifested air cargo).

Air cargo – owners can arrange for their animals to travel as air cargo without making the journey themselves.

So whilst the AlItalia WEB site does say you can take your pet in the cabin - it also says:-

In order for your pet to be able to travel with you, you must buy a ticket for it. The ticket fare depends on the pet’s weight, on whether it will travel in the cabin or in the hold and on the departure and arrival airport.