If you are a visitor, you might have more luck explaining your locking folder, but I would fully expect you would lose it if the situation were to arise. If you don't, you are lucky. With the increase in searches in London, and the introduction of more metal detector for trains, even as a visitor I would not want to try my luck wandering around with a lock knife.
There have been enough cases of UK residents getting very rough treatment from the law for carrying multi-tools, non-locking knives that make an audible click when opening, or bushcraft knives, packed in rucksacks full of camping kit, on the back seat of the car, going down the motorway. While the law says you are able to carry fixed blades, or lock knives, with a good reason, and sub-3-inch slipjoints anywhere, the law also allows the police to confiscate anything they don't like the look of.
I have never had a problem bringing knives into the UK in my hold luggage. The checks made by Customs are a bit hit or miss and I have only been stopped once, and that was because I had a rifle case. Zero problems. Out going security have looked in my suitcase twice and the 3-4 sheath knives didn't even raise an eyebrow.
Hunter Gatherer,
Not wanting to get into the politics of it, but the government isn't in the least bit concerned about armed revolt. It is all to do with an attempt to prevent crime. There is a certain logic...police on the street catch someone after there has been a stabbing, they might well be able to connect the person to the crime, but the victim was still stabbed before they could do anything. If the implement used to commit the stabbing was illegal, and the police could have arrested the perpetrator before hand, the victim would be saved. It is also felt that there is a deterent value in handing out 5 year jail terms just for carrying something pointy. When many people don't/won't even carry a Swiss Army Knife, such legeslation doesn't impact that many people.
I doubt that many people on this forum would agree with the above "logic". I do not, and feel very strongly about the whole issue, however this isn't the place to get into a political debate or rant
.