If you have been unlawfully arrested, you can pursue a claim for false imprisonment as well as assault.
If you are the victim of an unlawful arrest, the time spent in custody is classed as being false imprisonment. The amount of damages that could be received would depend upon how long you were unlawfully detained against your will.
Further, if you have been unlawfully arrested, you can automatically claim police assault if you were handcuffed or if unreasonable force was used during the arrest. If your case is successful, the damages awarded would depend on the severity of your injuries – whether they are physical or emotional.