I assume this figure is pre the addition of any bonding in this house, but what about the neighbours - they may well have bonding from MET to water pipes. even if external gas is plastic. Actually 1k2 sounds very high for that, I;d hjave expected single figures to sub ohm.

Water in 15mm or 22mm plastic pipes, unless undrinkably contaminated (and with the various treatments, pipes in heating systems can be) will be tens to hundreds of k ohms per metre of length, so there is at least one parallel path.

M

"although in theory the water does not need bonding."

Why not - if it is lead?

Geoff,thought if it could not be touched by the customer in normal circumstances, being 1metre below floor level and the lead being 300mm long,it would not need bonding.

1.2k seems very low for 1m of plastic pipe - I did some experiments a few years ago and (from memory) was getting around 15k from a single push fit fitting between two pieces of copper pipe - i.e. through just a few mm of water.  I suspect there's something else providing a path somewhere - is there copper after the stoptap and does it go anywhere near damp masonry or back underground (e.g. to feed an outside tap)?

   - Andy.

Ok. 

Yes Andy,as in the OP gas and water pipes are joined at the boiler and the gas pipe exits thro a brick wall,so I suspect dampness in that wall.

                                         Hz