Do all British schools require such strict dress code?

Yes, school uniform is almost universal. In high school (11-16 or 18), it's usually a blazer, shirt, slacks or a skirt, a tie and sensible shoes. Most schools let you pick up stuff like shirts and trousers from places like the supermarket, but there are also the school uniform shops. I think new rules have been brought in, but my experience with my son at high school was that we had to go to a specialist school uniform shop. That's where we got his blazer, tie, and his sports kit. Sports kit included shorts, tops, socks (in house colours), and jogging bottoms. It cost a fortune! I had to budget a minimum of £150 for the start of term. The idea of a school uniform is allegedly to give a sense of discipline and to prevent those from lower incomes standing out and being bullied. There's always something though, like getting the right brand of shoes. In addition, it can vary between schools. My son went to a seriously academic school that was hard to get into. The cost of his blazer was almost exactly double the cost of the blazer for the high school nearest to his, which didn't have the same reputation. It was a way of selecting, by making some uniforms a lot more expensive than others. Primary schools (4-11) also have school uniforms. It's usually skirt/trousers, a polo top or shirt and a jumper, no tie. I bought all of my son's kit from supermarkets, but the school did sell monogrammed stuff that they encouraged parents to buy. My son went to a sixth form college (16-18) and I was never so relieved that I no longer had to buy the uniform!