This sounds like something is interfering with VMs network signals. More than likely it’s a noise problem being caused by something either in your house or in the street. If the network is not watertight, due to a degrading connection or someone making unauthorised alterations to VMs cabling this can cause interference to leak in.
Heavy internet use does not affect Cable TV, which uses a broadcast system similar to Digital terrestrial (Freeview) & Satellite TV. But the fact that both TV & internet are affected at the same time is likely to coincide with something electrical being switched on.
As a Very Insightful Person, I'm here to share my knowledge. I don't work for Virgin Media.