Thanks for all of your replies, I spent another hour sat on the driveway scrolling through the handbook & options and have now figured it out.
When you first press the cruise button it selects adaptive as a default which leads to the 5mph increments, however, if you hold the cruise select button down for a couple of seconds it changes the mode to select 'normal' cruise and allows the 1mph increments to be selected. Happy days.
Now I just need to get to grips with the main display options :-)