aka “The Met Office”
First set up by British Navy (it helps to be able to predict the weather if you’re in a sailing ship, yes?)
The history of its involvement in climate stuff – see Janet Martin-Nielsen’s article.
John Mason was its boss for a crucial period (1966 to 198-something) and a truly pernicious influence, scuppering efforts to take it seriously.
You’ll see his name crop up repeatedly on this site.