This link seems to suggest that O2VM will by 2033.
Virgin Media O2 has confirmed that it will begin switching off 3G services in 2025 The move will allow the company to...
news.virginmediao2.co.uk
I can't seem to find any (reliable) source on the other networks and their plans for 2G. I read one place that said they "have to" shut off by 2033 but I really doubt that. I don't think ofcom or anyone else is forcing them to do this.
Granted 2033 is 10 years down the line, but we've had our electricity meter since the house was built in 1999 so it's lasted 23 years and counting. The smart meter replacement cost billions to bill payers and will likely cost more billions to replace again