Although I’m not conversant with the details of British law, in the U.S., “sexual assault,” as opposed to “sexual battery,” “rape,” or other charges, need not even involved physical contact. It’s a criminal charge that can be the equivalent of “sexual harassment,” the civil cause of action.
We often see the word “assault” and think it means hitting, shooting, or other physical harm, but that’s often not the meaning in law.
The way it was taught to us in Oregon & California, was that 'assault' occurs when there is a credible or actual attempt to inflict bodily harm: i.e, throwing a punch or kick whether or not it connects.
Battery, OTOH, is actual touching, as in the punch, slap, kick, etc actually makes physical contact with another...whether that was the intended target or not.
One can assault one person; fail to connect, and also be guilty of battery by accidentally hitting a third party.
Example: A swings at B; B ducks, and C, standing nearby is struck A. Assault upon B; battery upon C.