TwoSeven: ...I am just wondering if it is possible to go back to using the Airport - if so, how?
Yes, but you'll still need the Huawei HG659 to do the vlan tagging and to run VOIP if you have a landline service with Vodafone.
To change the Airport Extreme to work with the HG659 go into Airport Utility and under Network change Router Mode to Off (Bridge Mode), then connect the WAN socket on the Airport Extreme to the LAN socket of the HG659.
I'm not sure which exact Airport Extreme model you're using, I think only the newest one supports 802.11ac, so you may want to use that feature (and maybe Guest Wifi) on the HG659.