Is that ITV-SD or ITV-HD? Only because there's a few quick checks we may be able to do with you if we know specific channels affected. Assuming ITV HD, then I'd expect ITV+1 (SD), Channel 4 (SD& HD), Channel 4+1 (SD) to also be affected.
In any case, if you've restarted your box once, then pixellation on live TV tends to mean your TV signal has issues, and you should report the fault to Virgin, they will likely need to arrange an engineer visit.
150 from a VM phone, or 0345 4541111 from any other phone.
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