Do I have to help the Police?

Basically someone's car got stolen and I have some footage of it on my CCTV. The car was found and the women has a new one on insurance. I refuse to help the police simply because I don't want too, I really do not trust them with anything. Anyways now I'm getting police calling me, visiting me, asking nicely, asking badly. Can they do this?

Added (1). Its more of a "all the cr*p you done to me why the hell should I help you".

Added (2). Also I remember one time they wanted my phone a iphone 4 (when they were new) to check contacts ect as my friend had some weed on him. It took 9 weeks to get that phone back, over 2 months having to still spend £45pm on contract for nothing. This is just one of so many examples, ya fair enough if they found something on it but they didn't.

Added (3). Another example the same Police station wanting the evidence had a huge go at me when this old lady got mugged right in-front of me. The Police station was about 2 mins away like you could see it, so I think I do the good thing and instead giving chase to the guy I ran to police. I go to the phone phone "QUICKLY! GET OUT HERE NOW! WE NEED Help As soon as possible!", "What's the problem sir?", "An old lady just got mugged! QUICKLY GET THE F OUTA HERE NOW!", "Sir DO NOT USE THAT LANGUAGE!", "Awww I give up".

Added (4). I start giving chase to the guy and then POLICE CHASE ME! It really sounds funny looking back on it but at the end of the day they literally helped that mugger get away only because I swore at them in panic.

Added (5). Ohh and all the "Your known to Police aren't you?", I think no not at all I never been to jail, I never been charged, I never caused you any problems, I have no criminal record. Still its like if I can't be bothered to wear nice clothes I always be stopped, they always want my name and I always get the "Your known to Police aren't you?"

I've just always thought "if I can ever help you I won't". Its like they can do WHATEVER they want to me and I have to bite sh*t and accept it

Added (6). Oh and when my door got kicked in. I go to the Citizens Advice and they advise me to call the police for a crime reference number and then give that to my landlord for him to replace the door. I call the Police "Oh Hello my door got kicked in and I need it replaced." Before I could say anything else "Oh what do you want us to do about it!"

Yes, they can.
You may be charged with "Hindering an Investigation or prosecution". Maybe even "Tampering with Evidence". It will depend on if They want to play hardball.
They may need a simple subpoena, or Warrant to Seize your CCTV to get the evidence they want. When Cops get vindictive you might not get your equipment back any time soon, and may find "Inspectors from Health and Engineering" frequenting your place of business. I have knowledge of drivers being stopped for various infractions too.

You could be charged with obstructing the police in the execution of their duty

Can they visit you and ask nicely or harshly? Yes. If you ever have a meaningful question, ask it