France and Britain have similarly sized populations, and for most of the post-war period had similar sized economies, with France being in the lead, especially during the trente glourieuses from 1945 to 1975.
Brexit Britain has now pulled ahead. Here is a table for the last 18 years:
Britain's economy in 2024, at $3.686 trillion, was 16.6% bigger than France's.
In 2019, the UK's economy was only 5.6% bigger than France's, a difference that could be accounted for by minor fluctuations of the pound and euro against the dollar.
In 2020, both countries experienced the covid lockdowns. But Britain was also hurtling towards Brexit. The transition arrangements ended on 31st December 2020, and from 2021 onwards, Britain was outside the EU's single market.
Britain of course negotiated a free trade deal with the EU, and hastened to do deals with other countries: Australia, New Zealand, the twelve countries of the CPTPP. In addition Britain unilaterally cut tariffs for goods (mainly food) which Britain didn't produce but imported from Africa.
On the regulations front, EU regulations started to be repealed. The Financial Services Act 2023 repealed a whole host of EU financial regulations, including the cap on bankers bonuses. The City of London continues to be the dominant financial centre in Europe, despite the EU's frantic attempts to lure business away.
Britain has also escaped the regulations the EU has enacted since Brexit. The Financial Times reported that since 2020, the EU has enacted 13,942 new legal acts, while Britain produced about 4,000 and the Americans produced 3,725. That is making a difference too, though Britain could do more to repeal legacy regulations.
When President Macron visited Britain in 2025 for a State Visit, he went on an undiplomatic rant about how Brexit was a terrible mistake which had hurt Britain's economy. Brits listened politely and didn't voice their thoughts about the French economy which is suffering from the decision to remain in the EU.