In odd finds on YouTube - One Fine Day (1979) https://youtu.be/il-rYX5T0jE?si=Ppl5YeIWtmdLRQPX

Dave Allen (yes, that Dave Allen) plays a melancholic estate agent tasked with selling an office block that has been on the market for a year, he camps out in it, high jinks ensue. By Alan Bennet, directed by Stephen Frears