Information on the Virgin speed increases:
If youβre an existing broadband customer on 50Mbps or below, 100Mbps or 152Mbps, weβll offer you an upgrade to our more powerful speeds of SuperFibre 70Mbps, VIVID 150Mbps and VIVID 200Mbps
So not the rumoured doubling. People with older super hubs may need newer ones but Virgin will tell you if that's the case.
The upgrade speeds are being rolled out from 1 October for the next 6 months.
I don't know if you accepting the upgrade means that your contract period with them starts all over again. That's something which you may need to find out if that's a concern.