No company first reached a US$1 trillion market capitalization on the London Stock Exchange; the widely reported first trillion-dollar company was Apple on Nasdaq in the United States. The London market has hosted enormous companies, but none established that original global record there.
Shell, formerly Royal Dutch Shell, has often ranked among London’s largest listings, while AstraZeneca and HSBC have also held prominent positions. Their valuations have varied with energy prices, currencies, interest rates, and sector performance.
This question highlights why exchange and company domicile matter in market-cap claims. A business can have shares traded in multiple countries, and American depositary receipts can create a second trading venue. Record statements therefore specify whether they mean a company globally, a national market, or a particular exchange.