I need to install bonding to the gas services in a flat above a shop that has two electrical supplies and two gas supplies. The flat was two separate flats that have had a door put in between them, essentially making them one flat. Half of the flat is supplied from a single phase supply and consumer unit located in the flat, the other half is supplied from one phase of the shop's three phase supply, located in the shop. There are two boilers in the flat, one with gas supplied from a meter located in the flat, the other boiler supplied from a gas meter located on an external wall. (I think they have a common water supply, but haven't been able to confirm this yet. There is a 10mm bonding connection to the water supply). I presume this all needs bonding together? I am not sure on the best approach. Can I run a 10mm bond from the consumer unit to the two gas pipes and another from the 3 phase board to both the gas pipes? Or one bonding conductor from the consumer unit, to both the gas pipes, and then to the 3 phase board?