Swiss Army Knives are available to buy at several "Duty Free" shops at LHR and other airports.
Since seeing them there, I've never bothered to put mine in checked in luggage, now I always leave it in my laptop case (which is where it lives). Security in the UK, Germany, France, and the US have all seen it and ignored it.
And let's be honest, a broken bottle would be a much more dangerous weapon.
Mik