Hi Dawn,
Your version of events will undoubtedly differ to that of the Police. That's the first thing.
You quite clearly haven't given the full circumstances as to why they came to your home address. I speak from experience.
You don't say why your partner was arrested. And you don't say where you were arrested - in your home or outside in the street?
When they took you to the nick and you were still in the van, they obviously gave you the choice of the fine or being booked in and detained. You opted for the fine and were then obviously de-arrested and released - yes?
Police are allowed to use as much force as is necessary in the circumstances in order to effect an arrest.
If people fight, struggle etc, they may have to be forcibly restrained which can include being handcuffed.
If you believe that you have visible injuries caused by being arrested, you should go to the Police Station concerned, inform them that you wish to make a formal complaint, make a written statement and make sure that your injuries are photographed.
Don't forget, though, as I said earlier, the Police version will be different to yours, so unless you're adamant that they acted inappropriately, you may face an uphill struggle unless you have any independent witnesses of your own willing to back you up.
Consider carefully.