For any of those who purchased two 1TB TiVo boxes at £149, I have just had a response to my email from VM regarding the refund amount.
They have confirmed that I shall be receiving £100 credit on my account within the next two months, £50 for each box. I thought that is what they would do but didn't want to count on it until I had confirmation, which I now do by the way of an email.
Thanks VM