The whole point of a TT supply is that there is no earth terminal provided by the electricity supplier so it matters not one whit if the street cables are SNE or CNE.. If there is any connection to a  DNO earth terminal, it is not TT.

The neutral will have company electrodes in the street of course but they are one component of your 200 ohm or so reading, though hopefully no more than about 20 ohms or so of it and probably quite a bit less. Hopefully most of the 200 ohms is the local house electrodes.

However, if there if there is a low impedance between N and CPC on any circuit, rather than N and terra-firam earth,, then there is most likely a real problem, such as a short from neutral to metallic plumbing, or perhaps could the lighting circuit supply an outside light screwed to something metallic that is solidly earthed outside - fence posts, bollards that sort of thing ?

Mike

the odd thing was ,i took out all the neutral's and had a dead short between neutral and earth i then switch of the main isolator and the dead short went

With your  N connected to the supply (i.e. with main switch in the ON position) - N will always be connected to true earth via the supply arrangements (N is deliberately earthed at the transformer at the very least - often at many more places too via additional PME electrodes and other consumer's bonding). So there will be some continuity from N through true Earth to your TT electrode and hence to your Earth bar - in the region of your 205 Ohms - or 0.000205MΩ - which will show on most insulation meters as 0.00 or a dead short.

   - Andy.

No issue with metal boards as such - it was just that split load units are normally supplied with single insulated internal connections upstream of the RCDs - which probably isn't a good idea on TT.

   - Andy.

When Paul Berryman said that he had a "dead short" I took it to mean that he had used a low resistance ohmmeter rather than an insulation tester.

However, why was a dead test done with the main switch closed? (I am asking him, not Andy.)

because its a split board and there is two rcd after the main switch