Fortunatley i have never been on the wrong end of the law (1 speeding ticket ommited!)
Like you Jon i used to carry the Victorinox version of your leatherman with me everywhere i went. It turned out to be useful in so many situations it would be impossible to list, but they ranged from removing the spark plugs in my friends defunct land rover to unplumbling a washing machine!
I must admit now however i have stopped carrying it unless i am out in the fields although the blade is under 3 inches. I just don't think that if i were stopped the 'just in case' defence would cut the mustard with the police although i would imagine i would get no more than a warning for a first offence so to speak.
Out in the fields would be a different story and telling any officer about your hobby and why you are carrying a knife would i have no doubt not concern them at all. Indeed the dog unit exercise their dogs in some of the fields near me and none of them have ever challenged me about wearing a knife when i have met them.
Having worked with the police a few years ago i would imagine that getting stopped and searched without reason would be highly unlikely. These days they have to fill out an "encounter" form if they stop you, the paperwork is immense for these situations and most officers i know most would not stop you unless they had VERY good reason to as it is in their words "just too much damn hassle"
"They couldn't hit an elephant at this distance."
Famous last words of General John Sedgwick
May 8th, 1864