Well most of the times in America are related to daylight Saving but here they are as standard:
AST (Atlantic Standard Time) = GMT - 4 Hours
EST (Eastern Standard Time) = GMT - 5 Hours
CST (Central Standard Time)= GMT - 6 Hours
MST (Mountain Standard Time) = GMT - 7 Hours
PST (Pacific Standard Time) = GMT - 8 Hours
AST (Alaskan Standard Time) = GMT - 9 Hours
i am not too sure when Daylight Saving is but you just take one Hour off of each.
and of course the other way round for the UK - but that wont be needed i wouldnt have thought.