My clamps have padlocks through them when the ladders are on overnight or unattended in suspect areas. But if someone really wants them then they will find a way to get them. I can think of at least 2 methods which will bypass the security of the padlocks... 
Hi Ian,
I have got some clamps from Midland ladders for £20.00 which included locks & P&P, & I have a garage aswell to keep my motor in, so it will be secure overnight.
I think I am going to have to get another set though. I am just thinking about the time, hassle, spinning clamps up & down & locking them, whilst using just the one set.