Off duty officers can place themselves on duty at any time should the necessity arise.
Searches of outer garments can be done in public.
Searches of inner layers of clothing can be done out of sight of the public - back of a van, behind a building etc
Strip or intimate searches should be done in private circumstances, most usually at a Police station or other secure location such as a hospital under strictly controlled circumstances: supervised, same sex officer, multiple officers etc.
So the answer is - Yes, if he placed himself on duty and the other circumstances were met. But it would be highly unusual.
Please bear in mind my knowledge is several years out of date and the recent legislations may have changed that.