A) Yes, "I have just been to the shops" is what we say in BE. "I just went to the shops" is not incorrect, but it has a different meaning, something like "I only went to the shops"; C) "You was" is not considered good English, it would be on a par with forms like "ain't"; "you were" is proper English; D) "Media" is plural; occasionally you might come across it treated as singular, but it's not correct usage; B), E) Collective nouns, including company names, can be treated as singular or plural, depending on whether you want to emphasise the whole or the individual parts which constitute it. So both "the crowd is" and "the crowd are" are acceptable according to the context. However, plural agreement is more usual with certain terms, such as "government", company names, bands, sports teams, etc.

Your most valuable responses will come from BE speakers, but, as a fellow American, I can vouch that we are often somewhat sloppy about this counting thing. For instance, no one would likely bat an eye at "A multitude of journalists are waiting outside the door" when 'multitude' is clearly singular. I suspect it has something to do with the simple proximity of 'journalists' to 'to be'. Perhaps the variation in what verb form follows 'multitude' and 'crowd' comes from our use of 'people'. Althought 'the people' represents a single collectivity, we still say, "the people are". Thus, similar to my example with 'a multitude', one might say, "the crowd of people are". Although, I think this is incorrect, it might suggest how 'the crowd are' comes to be used. To my mind (and in my usage) 'media' is clearly plural as it includes all sorts of media such as print, broadcast, online, radio, etc. To my mind, those who say, "the media is" are not clear about the origin of the word nor the derivation of its plural. It seems to me that most of the English words that use a latin based plural (e.g. cactus/cacti, antenna/antennae, speculum/specula) are scientific or technical words. English speakers that don't live with such terms are less likely to use them comfortably. One day, we can expect to hear "the medias are". As for 'BP', since petroleum is an uncountable noun, I have no idea why one would say, "BP are". Again, some British input would be helpful here.

Sorry, that last line should say: E) Same with company names. We say "BP is..." and they say "BP are"! They really restrict character count and I was editing like crazy and hit Send too soon. :-)