Delay in page opening

Hi I’ve just recently had my M350 fibre broadband installed and all speed tests are coming in at 384Mbps so I can’t complain with that but there is a long delay when opening any web pages with some not fully loading at all. Settings have not been changed on the hub which I belive is a hub 5. Does anyone have any ideas why I have the delay? I notice there is a virgin firewall which is active, could this be the issue as my old much much slower bt setup didn’t have any firewall other than that installed on my laptop. The delay is on iPhone iPad and windows laptop all connected wireless