Nellie, the kirtle is a pain. The ones that were worn by Princesses had become very stylised, particularly in the example of Princess Augusta here. The peeresses wear something closer to the item in question, a full-length coat with short sleeves and a fastening at the waist, and I'm sure they'd be glad to see the back of them next time, as they were the Court feathers and veils after 1911.

In the photo below, you can see the Mistress of the Robes unhitching the hooks and eyes on the parliamentary robe, thus releasing those straps. This is a film, starring Lavinia, Duchess of Norfolk (Bernard Marmaduke's wife), that was made as a test by Pathé in May 1953.