Surprisingly, there is no law declaring English the official language of the UK.
In fact, English is just the de facto official language of the UK, which means it is not legally sanctioned as official but spoken by the majority.
England and Scotland do not have any official languages. Northern Ireland’s official languages are English and Irish.
Loads of stuff in the UK is not set into law but rather into custom iirc. So instead of “because the law says so” they have a bunch of “because we’ve always done it this way”.
Turns out that’s how a lot of the US government functions as well. We all saw how that worked out.
Unfortunately we are fighting against that effect too. Thankfully it’s not as effective over here. A lot of our customs and culture are deep rooted, historically. This makes it a lot harder to overturn, without creating problematic ripples. It’s not stopping them trying however.
As the saying goes. In America, 200 years is old, in England, 200 miles is far. A lot of our customs have been shaken out and tested over the centuries. They still exist because they both work and are hard to dislodge. America’s government is a lot younger, and was made as a whole. This leaves it a lot more brittle, and so easier to break.