Goes back decades to when the rot set in and we started the decline in UK manufacturing, with all kinds of things being manufactured abroad (particularly the far East) instead of in the UK. That just means money flowing out of the UK, i.e. the balance of payments deficit. That caused unemployment and we didn't sell as much exports to other countries, so less money coming in, and again, increasing the balance of payments deficit.
Politicians papered over the cracks by claiming we were becoming a service industry and lauding London's financial services industry, etc., but that's just "funny money" and has cost us billions with the financial crash, bank bail-outs, etc.
As we saw during Covid (and the Suez blockage), we're now far too dependant on imports, and that damages our economy when the flow of imports is disrupted. As we also saw, a huge proportion of our economy disappeared for months as the service industry (hospitality, leisure etc) was virtually closed down and cost billions in furlough and other support. Whereas our food and manufacturing industries carried on throughout with much less disruption as they were "essential" so could carry on.
It's part of another massive shift of wealth from continent to continent. History proves that "empires" ebb and flow. For a couple of hundred years, the "west" has been wealthy, mostly at the cost of poorer countries. Now as manufacturing/tech etc has moved to the far east, the "wealth" is flowing away from the West to the East.