Are you currently here in the UK with a UK billing address on your account ? If you are you should be able to download it. If you are here and haven't yet changed the country and put your UK billing address and payment details on your account : Change your Apple ID country or region - Apple Support
Or if you are still in Italy does their app in the Italian store do what you need : https://itunes.apple.com/it/app/area-clienti-3/id436132627?mt=8 ?
If you need the app that's in the UK store and you aren't here to download it, try contacting Three and ask them to put it in the Italian store.