I haven’t been following this. What will change in GB?
LOL, they can make their own rules about how to make and consume Cotswold.
The most important single thing about Brexit is that it preserves British sovereignty. While the United Kingdom is still, currently, a sovereign nation, membership of the European Union has been slowly eroding that status. When the UK joined the EU, it was still, more or less, a large scale trading organisation. Since that time, though, the EU has moved more and more towards because becoming a single state and it has become clearer and clearer that the aim of the many of the EU is a single "United States of Europe" where individual nations would be less important than they are now.
It also allows the United Kingdom greater power to secure its borders. As part of the EU, the UK is obliged to allow residents of any EU country, more or less free entry to the UK. This might not matter if that simply meant that established Europeans could move freely into the UK - but when you have some European countries granting residency to large numbers of 'asylum seekers', it basically means other countries currently get to decide who can enter Britain.
The EU is also very bureaucratic and regulation bound and imposes all sorts of trivial regulation on its members. At times, these regulations are in conflict with historical British interests, and traditions.