Starting next week, please help?

Hi, I’m supposed to be becoming a supply teacher for secondary schools as of next week. How formal are dress codes at state schools nowadays?

I’m thinking of wearing black suit shoes, black/blue suit trousers and a shirt without a tie. Are ties really needed to be worn nowadays? I also, don’t own a blazer and am wondering if I’d need one?

Also, I have a rucksack that I would usually carry my stuff in, or do I need a smart briefcase or something?

Thanks in advance