Is it illegal to put patches on my dogs coat

i live in the uk and I was wondering if it is illegal to put k9 in training on my dogs coat not to gain acces to places just to wear them?

I doubt it's illegal. Ignorance of the law is not an excuse for breaking it (if you try and get in trouble, saying, "I didn't know." won't hold up in court) but if I were you, personally, I would risk it. I mean chances are, if it is illegal, someone will just tell you to stop.