On Tivos here in the US, they don't have a switch.
On the back panel, near the jack where the power cord plugs in, there is a sticker with various information, like model number, TiVo Service Number, manufacturing date, and other stuff.
I have no familiarity with UK TiVos.
But there's a section specifically dedicated to the Virgin TiVo
where you should post your question, 'cause the people who hang out there all have that kind of TiVo, and if anyone can give you an answer, they're the ones.