on paper, it would be quite easy to get away with checking a record such as you describe (although GUM clinic records aren't usually kept with the general record) On the spine system such an access would immediately be noticed and flagged and the person would be dealt with most severely.
Literally you can lose your job (and clinical registration so no more nursing job EVER) and never ever get anykind of reference that doesn't include that unauthorised access, you would basically be kissing goodbye to ever working in health (NHS or private) again plus i can't think of many other places who would employ you, that one misdemeanor would follow you everywhere.