Olivia Colman (Debbie Doonan) & Meera Syal (Aunty Hayley) also worked together on seven episodes of Broadchurch (2013) as Ellie Miller & Judge Sonia Sharma respectively.
The 'Gash' of the episode title, while at first glance many would see a relatively rude slang term, refers to a head wound Simon gets when he impulsively jumps off the roof.