You'll have so much fun. I took my Mom & MIL last October. We did 'dress' up a little more (I wore a sundress, moms wore capris and a nicer shirt), but I've seen others in t-shirts & shorts too. We had the Buckingham Palace and I think I had the Eros tea, which was
and I'm not much of a tea drinker. I'm taking my BFF in June and plan to have the same thing although I don't plan to dress quite as nice this time.