The UK has a hopelessly unbalanced economy, with "financial services" and arms sales providing the bulk of GDP.

Without those the rest of the UK is an economic wasteland, relatively speaking. Outside of London and the Home Counties most of the population is ridiculously poor.

The UK is actually good at law, finance, the arts, and STEM. There's also a significant "boutique" export sector of high-value items of various kinds. There could have been a significant mix of intellectual/service activity and industrialised production, but most of the latter was sold off and shut down in the 80s - often to foreign corporations.

Brexit has severely damaged all of the above even further.