Inspired and based upon by the true story of the 'Hampstead Hermit', Harry Hallowes.
After his death in 2016, Harry Hallowes' half acre of land was bequeathed to two homeless charities who put it up for auction. The land sold for £154,000.
Jason Watkins (James) and Hugh Skinner (Erik) also starred together in the BBC comedy series W1A (2014).
Donald says he was born in North County, Dublin. Brendan Gleeson was a teacher of English, Irish and physical education at the former Belcamp College Secondary School in North County, Dublin.
In the end credits the title of the Spanish traditional song "La Cucaracha" is misspelled as "La Cucuracha".