If there's any specific channels that you can identify as being particularly badly affected (including HD? SD?) this can help narrow down the issue. But otherwise, if you've restarted your box once and checked all your connections are finger tight, it's time to report your fault to let VM investigate and fix it.
If you have a VM landline, call 150 - otherwise 0345 4541111 - follow the options for "I have a fault with my TV service"
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