The Cambridge Vampire - Ronald Seth tells this story so it must be true...

Although he chooses some odd names for the characters and some odd phrasing as we shall see. In the late 1920s a a Peter Grimes (let the reader understand the name) lived in Peterhouse College, Cambridge and had ground floor rooms overlooking the disused graveyard of St Mary the less (or Little St Mary's Church) from the west end. One night he didn't sleep due to scratching on his windows and a fellow student told him about the reputed vampire in the churchyard - the only one left in England. There was nothing near the window to cause any scratching, no trees or bushes and anyway the scratching stopped when he turned the light on. A friend suggested that mice might be a possibility but the scratching sounded like glass so mice behind the skirtings were unlikely to make that noise.

 
A picture of the west end of the churchyard today - note the vampiric looking cat. 

 Anyway poor Peter Grimes got teased about this as it became common knowledge. But thankfully the scratching also died down. Come the day before All Saints Day, called, with no prayer book justification, all hallows even, when the dead are reputed to walk the earth (although how would they know what day it was when they are not bound by time as we are?). Grimes went to bed as normal but the scratching began again. This time when he put the light on it didn't stop. Grimes found himself drawn to the window, or so he said whilst in hospital in a state of severe shock. He thought it was the boys from the town making a nuisance of themselves, or a fellow collegian having a 'rag' [practical joke]. He went to the window and the scratching intensified, and started to be accompanied by grunts as if the entity was becoming excited. Grimes shouted at the thing to go away or he would call the porter. the thing became more excited at his words. Grime's hand went to the window catch and found himself opening the window. A clawed hand grabbed his wrist more like an eagle's talons than fingers. He caught a glance at the creature's face which had intense eyes and a mouth with two large fangs protruding from it. Grimes stated it could not be a mask. The marks on his wrist lasted a year and, until he graduated (in Seth's words) he was 'as nervous as a highly strung hare'. And here is a picture of the range of rooms in Peterhouse College viewed from the church yard.