Who Shot Barbara? - S4.E6

Barbara rows with Ted,accusing him of spending too much time doing DIY for Neil's girlfriend's mother,an old flame of his. She also falls out with Linda and Martin after she baby-sits for them and accidentally sets their kitchen on fire. Neil is unhappy with her when she frightens his girlfriend off and,needless to say,she is not popular with the patients at the surgery or anybody in the street. So...who shot her in the bottom with an air-rifle?