I have seen the light. Here are the rules:
1. If a team has 2 bits to it's name then it stays the same, eg Tottenham Hotspur, Manchester United, Manchster City, Bolton Wanderers.
2. If the name has no relevance to the place, then the place name is used as a suffix, eg Arsenal London.
3. If the name is a town or district/borough etc then you stick FC in front of it, eg FC Chelsea, FC Everton, FC Liverpool.
UNLESS...
4. The name has 4 or more syllables in which case it stands alone, eg Middlesborough, Wolverhampton.