This has been a common theme after the proscription: The police has repeatedly abused the proscription to go after people expressing opposition to Israels actions in Gaza, without mentioning PA.
The excuse for that is that the Terrorism Act is not limited to making direct, overt support illegal. Section 13 makes it illegal to wear an item or clothing or wear, carry or display an article in such a way or in such circumstances as to arouse reasonable suspicion that he is a member or supporter of a proscribed organisation.
This has multiple times been interpreted by the police as justification for threatening arrest over expressing support for Palestine, and the government has done nothing to stop the police from drastically overreaching in this way.