I bought a cheap smartphone from Sainsburys, but I switched all unrequired services off, so no data, no WiFi, Bluetooth is off, location reporting is definitely off. I only got it because it charges via micro usb.
If virgin need details give false ones and pay with cash. If you get spooked, then pay a tenner to unlock the phone (or DIY if you're savvy) and buy a 99p SIM from a supermarket.
As other threads have mentioned, the phone is the one piece of kit where you have to be meticulous. Has anyone watched Hunted on C4 recently?