36 Mortimer Avenue
From Tardis Wiki, the free Doctor Who reference
Graham and Grace O'Brien, lived together in a house in Sheffield with Grace's grandson, Ryan Sinclair. Following Grace's death, Graham and Ryan continued to stay there when not travelling with the Thirteenth Doctor. The house was number 36 on its street. (TV: Arachnids in the UK)
Behind the scenes
In the real world, the Sheffield house which stands in for Graham's house is located at 36 Shrewsbury Road, just outside the entrance to Park Hill flats. In Arachnids in the UK, Ryan says to Yaz "Wait you live at Park Hill? We're just up there", implying that the house is just up the road; this lends credence to Graham's house being located in the same place within the DWU.
