For what its worth the Oxford Dictionary of Law defines a weapon of offence as "ANY offensive weapon or any article made adapted or intended for incapacitating some one." It also mentions a special offence "Trespass with a weapon of offence" It defines an Offensive Weapon as "Any object made, adapted or intended to be use to cause physical injury to a person." Examples given include revolvers, coshes and daggers. It goes on to say that under the Prevention of Crime Act 1953 states it is an offence to have an offensive weapon in your possession in a public place. It then mentions "without a reasonable excuse." Basically as far as coshes go I would suggest that even wooden weapons could end up getting you in trouble. So I wouldn't risk it. However if you a clearly sober and a martial artist and clearly training it seems likely the police might just tell you to go home and not do it again. Though metal weapons could get you in serious trouble.