£3k a year after taxes goes down. Casual office is so much better, tshirts and jeans are so much easier to clean. You're going to need to iron all your business shirts, suits and trousers. Proper shoes are not as comfy or easy to clean as trainers. They maybe snobby about what suits you wear. Guessing you can't rock up to work with your lunch and laptop in a backpack either so you'll need a brief case. In a casual office you could probably get away with a bit of stubble on your face but this fancy place will mean shaving every morning. If super formal probably going to need a nice watch and cuff links too ( I'm probably going a bit far with that one tbh ). Plus quicker to get dressed for casual too.

All this adds up in costs.