Seekerz:
We were only required to wear school uniform while at school, or travelling to or from it. I've never heard of any requirement to wear it at other times (unless, possibly, it was a boarding school?).
However, as I've indicated in previous posts, our school rules certainly extended to our leisure time. Playing soccer for an organised team meant automatic expulsion.
Quote from our PE teacher: "You will NOT player SOCCER" (with plenty of stress, and a look of utter disgust, upon uttering the final word of that sentence). "Soccer is only for common people. You are young gentleman and gentlemen only play RUGGER. Let there be no doubt boys, that I mean the game of Rugby Union. There is also a vile form of the game which is called Rugby League but that is also only for the common people. Remember, boys, that RUGGER is the name of the game and nothing else will be played or tolerated here".