Hi there,
I'm a planning officer so can give a reliable answer.
The Heritage Gateway is the newest official website which has all national and locally listed properties
http://www.heritagegateway.org.uk/gateway/
If a property is listed, it is the whole property which is listed. Anything attached to it can also then require listed building consent for alterations even if it is a more modern addition. However the listing will detail the items of specific historic value - which usually means these items cannot be touched at all, but other proposed alterations may receive listed building consent if done sympathetically.
The website can be a bit tricky to use. Its also worth remembering that the address may have changed since it was listed. Calling the planning department won't make any difference as they use the same website I just gave you. However they may be a bit more adept at using it!