The Leatherman Wave wouldn't be legal in London as it has a locking blade. The general rules are 1) no locking folding blades, 2) no folding blades over 3 inches in length and 3) no fixed blades of any length.

Leatherman Waves are expensive and I wouldn't want to risk it being confiscated at the airport or possibly at a railway or tube station. I believe there are also some metal scanners now being introduced on main line railway stations and London underground tube stations.

If you do need a knife in London then a basic non locking SAK will be fine as long as the main blade is less than 3 inches in length. It would be prudent not to display any knife in public (even a legal SAK) unless absolutely necessary.