I really don't think so. If you went to a first interview in a suit and everyone were dressed extremely casually (flip-flop casually) and then you dressed the same for a second interview, definitely questions might be asked. But on the whole in the UK I would say it's pretty common to dress smartly for a first interview unless you have specific information (eg. from a recruiter or hiring manager) that you should not do that.

If I were interviewing in finance, I would definitely wear a suit. If I were interviewing at a startup or a digital agency, or equivalent, I would wear smart trousers (maybe smart jeans) and a shirt. That's playing it safe. Sometimes I interview people who are wearing jeans and a t-shirt and generally look pretty scruffy - I know that they know that that is probably the attire most of their potential future colleagues will be wearing, but it certainly doesn't impress me much. But maybe I'm just old-fashioned.

I thought there was a lot of good advice in those slides, incidentally.

I always wear shirt and tie to the interview then ask about dress code as if they expect me to sit there developing suited and booted I'm not the guy for the job!