Her name is Daleside Vetch:
She was sired by Michael of Moreton, who was an early prolific stud in the breed. Her mother was a Speedwell dog, and the first golden retriever to ear a championship in the United States was Speedwell Pluto, who was very similar to this dog in type.
You can see the full clip at British Pathé, which shows a 1934 newsreel covering Crufts, “The Greatest of All Dog Shows.”
HT to Jemima Harrison for finding this one. I’ve had bad luck finding golden retrievers on British Pathé. Every time I’ve come across a clip of a supposed golden retriever, it turns out to be that of a Clumber spaniel!
You can see the flattie in there.