A bit of both, depending on the situation.
Generally I have observed that the English have a hard time turning down their bosses and colleagues for whom they have a lot of respect.
This is interesting, since this is something a lot of bluff speaking Englanders pretend doesn't happen, but...
Most English people assume that if someone says something is extremely tricky to do, then that will cause the person asking for it to reconsider. It is better that they withdraw their request then have it denied, which is rude and demeaning for the person asking it.
A lot of English people are not aware that they act this way, but is a part of polite behaviour that we learn by example as very small children.
Americans seem to have absolutely no comprehension of this. Saying, "No" to someone does not have the connotations it does in other societies. Apart from that, I can say that Americans in the South are charming and polite in all other matters.