BC, before you unscrew anything, make sure you turned off the water at the main.
have you got one of these, blue? muilti grips i thnk theyre called
just put a rag on the tap cover first to protect the finish
if it persists, spray a bit of WD-40 in there, or something similar...... perhaps theres a bit of corrosion....would help loosen it up
I found I couldn't get the bits off my kitchen taps, but that was mostly because of my arthritis - I've lost strength in my hands and one shoulder.
I found the answer though - I rang the Grey Army and got a handyman out to do the job. 
I have a pair of those, Joe, and tried them but still couldn't get the bloody thing to budge. i have bought a boa wrench but forgot the WD40. I'm having a coffee before I try it. I've turned off the mains. A few months back, one of the shower taps exploded and there was water everywhere. I was like a chook without a head until someone asked,"Ummm, have you turned off the mains?" I hadn't. Well, I am a blonde and I do have a reputation to uphold. So far I've been fulfilling that role remarkably well. 
Perhaps, I need someone from the Grey Army. I think that a little old man would have hands stronger than mine.
There aren't many male neighbours here and the few that there are, I don;t really have anything much to do with them because of my anxiety disorders.
No, no luck. 
The tap set was only installed about 8 or 9 months ago - the plumber must have the grip of a very strong person.
