They would hire anyone even wearing in a bin liner, your a number and can be gotten rid off as such, so it doesn’t matter, I got the job before even sitting down.
Officially code dress
It depends. If it's entry level you could roll up in your dressing gown stained with Stella Artois and still get a green light. However if it's more technical, maybe bring the onesie or perhaps the Adidas tracksuit.
A smart casual dress as a good impression, goes a long way.
When going on an interview at Adecco you should wear shirt and trousers.
For a man, trousers, shirt and tie. If going for senior role then a suit.