Recently moved from virgin media to community fibre

Previously had one deco connected directly to the virgin router and another upstairs. 

Have a single network on deco for both 2.5ghz and 5ghz. Used to get near predicted speeds on all devices (250mb)

Now community fibre installed I took the deco ethernet cable out of the virgin router and put it into the new router. Deco status light went red for a few seconds then white. 

Connected to the WiFi network on phone and other devices (didn't change the network name as thought no need) and ran a speed test. Am getting about 100mb instead of the predicted 500mb I signed up for. Switching to the community fibre WiFi network (and therefore taking the deco out of the equation) is giving me speeds of about 300-400mb. 

I've rebooted the deco network but no joy. 

Any ideas if I need to do some additional configuration? As ideally I need a solid network all over the house hence wanting to use the deco's

Thanks in advance!