Seems like forever since I have been on here!
I used to buy the OS maps whenever needed direct from OS. However, best thing I ever did was get the complete set of OS DVD's called Memory Map.
This allows me to either print off if necessary or for work I can plot a line between two references and show a direct line profile, see this for a job I did recently:
It makes short work of deciding if I need to survey, take a big aerial or not. In terms of visiting and walking it is also very simple to use.