Decomissioning the offshore wind turbines could get into the same range though, assuming £400M per installed GW (nameplate), this would be £3.2Bn
Numbers need to be taken with a large grain of salt.
The best I could find was a document by the National Audit Office from 2017 (using 2016 estimates); page 18, figure 2 - The expected costs of Hinkley Point C.
https://www.nao.org.uk/wp-content/uploads/2017/06/Hinkley-Po...
Back then the construction was estimated at £18.2 billion. Ongoing operation costs (including fuel, staffing, and grid charges) were priced at £29.3 billion and decommissioning (without the uplift) at £7.3 billion. Total project cost was put at £54.8 billion.
Again, it was from 2017 so things have changed.
Handling and disposing on the used fuel is 4.4B GBP (or 73M GBP per year of running, or 2.6 GBP per MWh of electricity). Cheap!