I have now had the TiVo box for 4 days. Unfortunately, on Wednesday morning the box decided to start a continuous reboot cycle which resulted in having to turn it off!
Having spoken to the Virgin Media technical support team (who are actually quite good once you get through to the dedicated TiVo support team), the earliest the could send an engineer out was Saturday. As a result, I have had to temporarily revert to the old V+ HD box.
Once the engineer has been out on Saturday and (hopefully) fixed the issue, I will set it all up again and see how it works for a few days.