Looks like an SNR issue rather than weak signal.
Check the white cable is screwed in tight to the back of the Virgin box, & wherever it is connected to the other end.
If these are secure then call 150 from your VM phone & select the option for faults.
Cable customer since 1993. Services: FH TV, Sky Sports & Movies (2xV6), Talk Anytime Phone, VIVID 350, Virgin PAYG Mobile