'Harald of Mayfair'
Like the broadtail dress, the 'Harald of Mayfair' evening dress would have been custom-made for Vivien Leigh. This particular item was made by the London-based couturier Harald Mahrenholz, who opened a fashion house on Curzon Street in the 1930s. Vivien Leigh's Harald dress was likely made in the 1950s.
This is not the only Harald item that Vivien Leigh owned. Her personal papers at the V&A record a number of other Harald dress items in her possession, including a tweet suit.
As you can see from the image, the silhouette has been altered to allow Vivien Leigh's daughter to wear the dress.