A while back I had broadband issues and discussion with engineer involved the fact that if 'all is well' within your home/network up to and including the VM Hub then there are probably problems with your signal. So some thoughts :
Have you had any discussion with engineer/VM customer services regarding Upstream and Downstream power levels. If those are not within parameters then you can get pixellation.
Even if power levels are OK you can get pre and post RS errors to a sufficient degree to cause pixellation - that cause of those error would need to be a VM engineer job and in some case can be that some parts of the cable between the VM cabinet and your property are damaged and need to be replaced.
Suggestion is to go for a discussion with Customer Services who can remotely check power levels and may also be able to comment on errors. If you have the engineers number then perhaps have that discussion and see.
Hope this helps - not a cure for sure but maybe a pointer or two.
I can see that some of you have already called in or arranged technician visits so if you're still experiencing issues with the picture just let me know what box you're using and whether it's affecting specific channels so I can investigate it further.