Can anyone join the navy/army?

I live in UK for 6 years, I'm 18, but I was born in Poland and don't have English nationality. I have bad eyesight (need glasses/contact lenses). I heard the requirements for all the military groups are extremely strict and some tiniest thing that you have can prevent you from entering, but I also keep hearing that 'Army is for everyone' and 'everyone has a place/role in the army' etc, so which one is it?