The law regading impersonation of an officer is one of those where you do not have to be trying to commit the offence, to actually commit an offence - confused : here's the sort of relevant science bit;
Section 90 of the Police Act 1996) creates offences relating to the impersonation of police officers or the possession of articles of police uniform,
namely:
impersonating a police officer (including a special constable);
making a statement or doing any act calculated falsely to suggest membership of a police force;
wearing a police uniform calculated to deceive;
possessing an article of police uniform.
NB: The words "calculated to deceive "means likely to deceive" and therefore the fact that there was no intent to deceive is immaterial.
Any person who, not being a constable, wears any article of police uniform in circumstances where it gives him an appearance so nearly resembling that of a member of a police force as to be calculated to deceive shall be guilty of an offence.
“article of police uniform” means any article of uniform or any distinctive badge or mark or document of identification usually issued to members of police forces or special constables, or anything having the appearance of such an article, badge, mark or document.
So, it could be put forward by any prosecutor that the sole reason you have the word POLITE, on the back of your jacket, and the particular colour combo you've used is an attempt to give at least a partial impression that the garment is actually indicating that it refers to police, bearing in mind that what the piece of legislation says is that the article only has to give the "appearance" and whether or not you intended people to think that is irrelevant.