I just want to leave a comment here as I'm interested in the answers! I have this problem too!

i grow mine in pots so i dont have this problem so i looked in my book for you and it said: lift up the runners{suckers} and use secateurs to cut away from the parent root.plant immediately where the new raspberry is to grow.do this usely in oct or nov time if you are raising new plants.
but i suppose if you dont want to use them you could just cut them off anytime.i hope thats what you ment.

Thank you Plantsmaiden - I would like to pot mine up so I'll wait till Autumn, unless they look like taking over!! Nice pup BYW ;-)