If arrest you for something you are not guilty, they just need reasonable grounds to do so. The TV van is just used to say we suspect they have no licence. I think when they knock down the door this is for more serious matters. However, with a warrant they can certainly enter the premises by reasonable force they just try and avoid it. If you have paid. you may not let them in, but you would show proof of payment, or you would show you have no TV, or you are not watching live channels. We all know if you make matters hard for them then you get found guilty you will get hammered.