In episode 7, season 1, of Humans, Leo and Fred meet in an unusual art gallery:
What gallery is it and where is it located?
It is the Marianne North Gallery of the Royal Botanical Gardens at Kew. The museum is located in at Kew Park in south-west London, UK. It was built in the 1880's to house the 833 paintings of Marianne North.
Here is a picture from the museum's website. You can see that the floor and the walls match the image from the show.
Another image from this website is larger.
Opened in 1882, the Marianne North Gallery pays homage to the artist after which this massive collection is named. The daughter of a politician, North travelled far and wide across North and South America, Asia and Africa in order to pursue her passion for painting plants and flowers. This stunning collection includes 832 of her paintings and is Britain's only permanent art exhibit dedicated to the career of just one woman.