Thank you to all the lovely ladies for your responses!
Yes, I should have mentioned that I am from a different country and have recently emigrated to the UK (some of you are really smart and guessed it already!). Back home, when you are shopping in medium to high-end stores typically when you pick an item off the rail one of the staff will walk up to you and will collect the item and keep it in the fitting room for you. And in all stores, low/med/high whether crowded or not, once you have tried on the item, you hand the discarded items over to the staff in the changing room (the hangers are already taken off the clothes before you take them with you in the fitting room by the staff at the entrance of the fitting rooms). Sometimes there is a big bin as well for you to leave the clothes in there.
So, when I was asked by the staff, I was taken aback, however I put the two items back on hanger and then was wondering about it while in the queue to purchase the selected item. I noticed that most people had hangers on even on the items that they wanted to buy (which I found odd TBH) and decided to check out here as to what is typically expected of you while shopping for clothes - hence my post :)
I am happy to go along with what is typically expected in a country.
Now, in response to some of the "holier than thou attitude" people - NO, I don't leave the clothes on the floor or "throw" them at the staff - I hang them on the rails/hooks/keep them on the sofa in the changing rooms while I am trying on and then collect my discarded clothes and hand them to the staff - as is expected of the customer.
NO, the store was not busy, this was Topshop, and surprisingly, just me and one other customer (who was told to do the same ) in their 10 -15 changing rooms, and the staff at the changing room entrance was just standing there and chatting up with the other staff) and did n't look too swamped at the time. Anyways..
Once again, thank you to the people who have responded nicely and in a considerate manner, this has been helpful :)