AJJewsbury said:

pipework carrying flammable and potentially explosive gas

not unless it is mixed with air/oxygen, on its own in a pipe it is neither

AJJewsbury said:

and whose continuity necessarily has to be broken on occasions during maintenance.

the continuity has to be kept in place by law, GSIUR reg 10

"Maintaining electrical continuity

10.  In any case where it is necessary to prevent danger, no person shall carry out work in relation to a gas fitting without using a suitable bond to maintain electrical continuity until the work is completed and permanent electrical continuity has been restored."

I use a car jump lead

But what 'electrical continuity' is supposed to be maintained when the gas company decrees that their extraneous-conductive-part supply pipe must not be bonded?

But what 'electrical continuity' is supposed to be maintained when the gas company decrees that their extraneous-conductive-part supply pipe must not be bonded?