There was a deal with Saxa Salt and there was blatant product placement in the film during one scene with Charles Hawtrey, this was unusual in the UK in the 1960s.
There were holes (due to rust) under the door of the car used in the film and water leaked inside during the rain scene. There was five inches of water in the car.
When Barbara Windsor did her first line and scene, Gerald Thomas immediately said cut and print as he considered it good enough to go into the film. But Windsor immediately said "I'll f***ing cut it, I didn't want to play it that way!" The whole set fell about laughing.