The attack upon Jason Ketley, who is bipolar and has a mental age of around two according to his mother, was only stopped after nurses spotted the rodent hanging from the 42-year-old\'s neck as he wandered down hospital corridors. After the animal was killed Mr Ketley was taken to Epsom General Hospital for diphtheria, tetanus and polio injections. Mr Ketley\'s mother Pat Boardman said St Ebba\'s hospital\'s claim a field mouse was behind the attack was \'outrageous\'. \'He had large, open bite marks,\' Mrs Boardman told the Daily Mirror. \'I\'m appalled that this sort of thing could happen to my son in an NHS hospital in this day and age. \'He was completely helpless and terrified. It\'s a disgrace. He was very scared and the staff had to show him they had killed the rat to prove it could no longer hurt him.\' Mr Ketley\'s parents have made an official complaint to Surrey and Borders Partnership NHS Foundation Trust over the incident, which occurred last November. Jo Young, director of quality and nursing at the trust, said a detailed investigation would take place into the claims. \'The events described here are genuinely shocking and I would like to reassure Mrs Boardman that we are taking her concerns extremely seriously,\' she said. \'Our records indicate that a mouse was seen in the house in November and that pest control was alerted immediately but we are unable to provide a complete response to all the concerns raised until we know the outcome of our investigation.\'