Switching off 3G and 2G networks: advice for IoT and third-party device suppliers - Ofcom
The plan is to remove 3G coverage across the UK by the end of 2024 and 2G by 2033.
In Germany, 3G went about 18 months - 2 years ago but the statement is that here 2G stays until the stats says no one is using it any more. Given that automated security devices rely on 2G, the chances are 2G will never go away here. All 3G phone fall back to 2G operation meaning calls and SMS are possible but forget any reasonable Internet data connection.
The 5G Cells equipment supports 4G as well. Indeed to bring in 5G into Germany, the existing 4G equipment was software upgraded from what I understand. Here one reason to close down 3G was to re-use the frequencies for 5G. I suspect there is the same reasoning in the UK.