It is to do with either the servers your boyfriend is connecting to or Virgin Media are slow again..
For me when playing games such as CS:GO I experience packet loss with Virgin Media as well which is very frustrating and I am currently awaiting a phone call back from them once the "fix" the connecting again.
My honest advice would be to call them to fix this issue. I would have a computer plugged into the router with an Ethernet cable when calling to make the call faster.
zoe82 wrote: My boyfriend keeps getting lag when playing online
Is the PS4 connected via Ethernet cable or wireless? Ethernet is best for online gaming.
Disclaimer - I don't work for Virgin Media. I'm just another VM user trying to help out so my answers may be wrong :-) If you do like my answer please mark it as helpful as it may help others My setup: Vivid 200 Optical fibre with Superhub 2 in modem mode connected to a Netgear R7000 router. Telewest/VM user since 2001.