This may be your reality but it has nothing to do with the truth.
Free trade in Great Britain began in earnest in 1820 and gained momentum with the repeal of the Corn Laws in 1846 and the Navigation Act in 1849. With the Anglo-French Commercial Treaty of 1860, the English practiced a largely free trade policy until WWI. During this time, Great Britain was the worlds wealthiest and most powerful nation.
In 1915, Great Britain officially became a protectionist economy when large tariffs were imposed on a wide variety of products. This was the beginning of their economic decline. The 20th century was marked by a dramatic increase in government control over the economy and, eventually, a welfare state. Protectionism killed the British empire, not free trade.
Really? Then explain please how a nation that was the largest industrial power in the world, hands down, pre free trade, couldn't build enough bullets and rifles in WW1 to fight Germany and had to import them from the US which was an anti-Free Trade nation at the time.