At a guess I think you might have an address conflict, but I think more information is required, and in particular whether the Beryl is in router or AP mode, and what your address scheme is.
The BT Hub I assume is your main router, so it is running a DHCP server handing out addresses to everything plugged in to its LAN port(s). Those are unmanaged switches, so everything plugged in to the switches will get addresses from the BT Hub. The BT Hub itself is going to be the default gateway, and most likely will have a xx.xx.xx.1 address. Let’s say for the moment that is 192.168.1.1, and it is handing out addresses in the 192.168.1.2-254 range.
The Beryl in router mode ordinarily has a LAN address of 192.168.8.1, and also runs a DHCP server that will hand out addresses in that range. So the first puzzle is how it comes to have a LAN address of 192.168.1.1, and how that fits with the BT Hub network. The switches are agnostic about what traffic they pass, I think. So the first thing is to figure out if the Beryl is in router mode and if you have two DHCP servers at work (a bad thing) and what their networks are.