I'm not aware of any actual events of such protests and burning of poppies.

In the absence of detail, I cannot comment on public protests without knowing what they were protesting about.

However, based on a hypothetical example, in principle I would certainly view burning of poppies as an inflammatory (pun unintended) and unnecessarily provocative and disrespectful event. The poppy represents those who gave their lives for our freedom and I do not see why anyone should wish to burn them as a protest. Legally, AFAIAA there is no offence, so I don't know if any charges could be brought.