Your advice would be a serious mistake in Britain as such action could carry a short stay in jail (a couple of years ago, a writer for a British magazine returned from a year in Italy and wrote of his predicament at Customs). If it wasn’t so sad, it would actually be funny; despite a stellar life (not even a traffic ticket), he now has a permanent record for carrying a tiny Swiss Army knife (the little Executive model). Welcome to the Nanny State.
In 2002, I brought a Kershaw Leek one-finger opening knife into Britain and received numerous friendly warnings not to display it. However, I believed it saved my life, or at least my wallet, one night in the city of Bath. As I was walking back to my B&B after dinner around 10 PM, two tall punks started following me down a poorly lighted street. I flicked my knife out and actually ran (I was 50 at the time) towards them. The last time I saw that much surprise in anyone’s face was when I put a shotgun to the head of a kid in my garage (that’s another story).
(grin!) it isn't quite as bad as all that, yet -- tho' it is rapidly getting that way.
Here is a link from the same Scouting website that summarizes the relevant UK law nicely.
Lawful Purpose would probably keep the Scouts out of trouble. What is Lawful Purpose? Well, cutting string and peeling oranges are "Lawful Purposes" for carrying a small pocket knife. As a Prepared Boy Scout should always have a piece of string with him, he should always have a Lawful Purpose for his pocket-knife.
My read of the Scouts' guidance is that their organization is acting from an abundance of caution, as the UK is experiencing a significant number of knife crimes. Once the gummint banned guns, the Crims armed themselves with bladed objects, to nobody's surprise...