A police constable worked near Cambridge in the 1970s. He was brought by Wilkin to St Cedd's College to investigate the disappearance of Professor Chronotis' room. The constable doubted Wilkin's story.
When they opened the door to the room, the room (really Chronotis' TARDIS) had re-materialised, and they barged in on the Fourth Doctor reading a page of The Old Curiosity Shop to Romana II, Chris Parsons, Chronotis and Clare Keightley. When the Doctor and Romana left in the Doctor's TARDIS, the constable told the others to get their coats on, as they were all going to "take a little walk with [him] down to the Bridewell". (WC: Shada, AUDIO: Shada, PROSE: Shada)