Instinctively, I'd want to check the HDMI leads & TV port first.. just to rule them out.
However, given this doesn't affect OnDemand or streaming...
1: Is this problem only on particular channels, in which case which ones? Including SD/HD?
2: Presuming you're recording these same programmes as well - does the same problem happen on the recording? How about if you pause the live programme and watch it slightly delayed?
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