It's certainly an 'interesting' analysis of the UK's position post-war which doesn't mention the fact that we were bankrupt on the war's conclusion and faced continual financial and currency weakness for decades. We ended up heavily reliant on the US virtually by necessity stemming from this.
The United Kingdom was indeed in dire financial straits after World War II but the overall economic situation wasn't nearly that dire and the country ended up paying for a lot of the capabilities it ended up losing anyways. GDP per capita was close to France until the late 1960s (source). The truly poor relative economic performance actually happened in the 1970s after the United Kingdom had achieved debt levels comparable to its peers.
Here is a graph of debt to GDP levels for various developed countries (from here):
In the nuclear field there was enough money to pay for the Sellafield Complex and Calder Hall and to develop and test both atomic and hydrogen bombs, but in 1958 the United Kingdom made the decision to rely on the United States for designing nuclear weapons and naval propulsion reactors. That's despite the fact that research and development costs represent a small percentage of the total cost of nuclear weapons and the fact that the United Kingdom has the second largest plutonium stockpile on Earth (source). Most of that plutonium is under civilian control but many of the Magnox reactors were built with the capability to run military fuel cycles, including three larger civilian stations (source). Even after outsourcing the development of nuclear technology to the United States the United Kingdom still had enough money to develop and build the Advanced Gas Cooled Reactor, a program that went significantly over time and budget. France took the opposite approach and developed its own nuclear weapons and naval propulsion reactors while choosing to base its Mesmer Plan reactors on Westinghouse designs that it developed into a French design lineage.
There was enough money to develop and technology in many other fields.
In aerospace there was enough money to develop three strategic jet bombers (source), an intermediate range ballistic missile (source), the advanced TSR-2 strike aircraft, the Vickers VC10 and Hawker Siddley Trident jet airliners, and pay for a portion of the Concorde project. Many of the commercial airliners that the British government and/or its associated corporations helped finance weren't commercially viable designs that needed some assistance to help come to completion but were essentially custom designed to the specifications of the state owned airlines, leading to difficulty in making international sales. The most successful British airliner of the period, the BAC One-Eleven, wasn't designed to the specifications of either of the state owned airlines and was launched with an order from British United, a privately owned company. It managed to secure orders from airlines based in the United States, no small feat in an era of protectionist aviation policies, including high tariffs on foreign airliners.
The United Kingdom developed the Advanced Passenger Train, the first with a tilt mechanism, and even had some enter service. It then cancelled further development and sold the technology to Fiat, which developed it into the successful Pendolino train.
Many early firsts in computing and communications were developed in the United Kingdom or by British scientists. The United Kingdom is still second only to the United States in the quality of its universities and is a major financial center, so it should have been possible to create a British equivalent to Silicon Valley. Even Finland was able to achieve major success with Nokia.
In Alternate History, there tends to be a habit of people liking a system or country so much that they write a story where it perpetuates itself until modern day and possibly forever.
I'm not talking about the British Empire, I'm talking about the the United Kingdom.
Bad luck doesn't even have anything to do with the decline of the United Kingdom, it's a series of bad decisions that happened for decades. That isn't something unique to the United Kingdom either. The Spanish Empire made bad decisions over the centuries before its decline, the Soviet Union made bad decisions over the decades that culminated in its collapse, and there aren't too many people arguing that the United States has been making great decisions over the past few decades.
France was able to steer itself into a preeminent position in Europe through good decision making after World War II. Russia has made an unparalleled comeback since the collapse of the Soviet Union. The situation for the United Kingdom was much closer to France and thus a similar outcome was well within the realm of possibilities.