abstract: Britain and England are not the same place. Britain refers to the mainland bit of the UK, which is made up of Wales, England, and Scotland. Great Britain includes various islands. The UK is England, Wales, Scotland and Northern Ireland. Thats why strictly you would say the UK, or "Great Britain and Northern Ireland" to refer to the same place.
Hence, refering to Britain as England means that anyone in Wales or Scotland will be peeved (and possibly also N Ireland), but is basically just inaccurate.
To be fair, plenty of English (and sorry, but yes, I mean English as opposed to including the Welsh or Scottish or Northern Irish) people refer to Britain as England, so how anyone in the rest of the world is supposed to get it right is completely beyond me!!!
It really wasn't meant as a furiously stroppy comment, so apologies for the offence!!