50
Virgin Media Warns UK Broadband Users Not to Switch Routers Off at Night - ISPreview UK
(www.ispreview.co.uk)
This is a most excellent place for technology news and articles.
It's only Virgin Media to my knowledge who does this.
Most of the other providers are happy for you to use anything that works properly for VDSL or FTTP.
Most FTTP providers fit an ONT that puts the connection back into an RJ45 ethernet connector.
Then you connect to the provider using PPPOE. Anything past the ONT, you can do whatever you like.