Yes, it is assault by beating, techkey, under s.39 Offences Against The Person Act
"The offence of BATTERY is committed if a person intentionally or recklessly on applies unlawful force to another person. Once again this is a very wide definition and does not have to result in injury. People are regularly convicted of common assault for spitting on another person. There is no injury but it amounts to a common assault by beating.
In order to be guilty of assault or battery, a person must either have to intend that physical force is used for fear, or being reckless as to whether either occurs."
http://www.professionaldefencelawyers.com/defence/index.asp?page=common-assault-and-battery-110
In the example you give the female was being held and asked to be let go. She was not able to free herself from the hold simply by stepping away.
If found guilty the likely penalty is a fine or conditional discharge, assuming the female suffered no injuries and this is a first offence.