Quite a bit of what you say doesn't make sense, But I believe with some clarification it may be an easy install, but if so I don't understand why BG couldn't install it. So maybe having seen the installation personally there's something they saw that changes it.
I have a Honeywell CM0970 controlling heating ( cable live and neutral only)
I'm not aware of this product, do you mean a CM907? If so it is a battery operated thermostat, and doesn't require a live and neutral. As
@ianmcd says, there are only two connections to terminals A & B, but they will be a 'live' and a 'switched live'. Maybe someone has used a blue or black wire for one of them and you have assumed it's a neutral?
and a Drayton LP522 controlling water.
This is odd. A Drayton LP522 is designed to control the central heating as well as hot water.
So it would be unusual to install one of these just for hot water control. Is the heating part connected to anything? Is the heating it set to be 'on' 24/7, and if so, what happens when you switch the heating part off? Does the heating go off even if the CM907 is calling for heat? If so, then the heating wiring is also connected here and a swap for Hive would be easy, like for like and the existing thermostat wiring simply bridged to complete the circuit.
I don't want a receiver and thermostat on the wall in my kitchen
A kitchen is one place that a thermostat should never be located, unless you never intend to cook in there. As soon as any cooking takes place, off goes the central heating to the whole house. The receiver can be located there for convenience, if that happens to be where the existing wires are located, and the wireless / battery operated thermostat would be located somewhere sensible
can the wiring be altered so I just have 1 receiver in the airing cupboard where the Drayton is without adding new cabling.
Thanks
The Hive Dual Channel version controls the central heating and the hot water from a single device. So, if the wires for the heating and hot water are located at the Drayton LP522, then the wires you need will already be there. If on the other hand, only the hot water wiring is connected to the Drayton in the airing cupboard, and the room thermostat is elsewhere the wiring that presently goes to the room thermostat will need re-directing to the airing cupboard.
Once you have provided the additional info a more definitive answer can be given.