The electrician said he didn't do the RCD trip tests as he said it couldn't trip with that resistance.

I'd agree that wasn't an accurate explanation at all (although I've heard worse when an electrician is trying describe electrical matters to a customer who may or may not be technically minded), and he might even not fully understand all the implications accurately himself and be over-relying on rules of thumb. Sounds like -1 for customer relations.  But even if his thinking is flawed, it doesn't necessarily follow that his final answer is exactly the reverse of what it should be.  The bottom line is I wouldn't want to give a clean bill of heath to TT system where there is reasonable suspicion that the earthing facility was showing signs of failing. As others have suggested, FI may well have been more appropriate than C2 - but both will give an unsatisfactory until more work is done anyway. If it's gone from 400Ω to 534Ω in the space of time between you both doing your respective tests, what's is lit likely to be in a month, at the end of the summer or next year? Can you really be reasonably sure it'll still be below 1667Ω? If not, how can anyone to state that the installation is satisfactory for continued service?

   - Andy.

The electrician said he didn't do the RCD trip tests as he said it couldn't trip with that resistance.

I'd agree that wasn't an accurate explanation at all (although I've heard worse when an electrician is trying describe electrical matters to a customer who may or may not be technically minded), and he might even not fully understand all the implications accurately himself and be over-relying on rules of thumb. Sounds like -1 for customer relations.  But even if his thinking is flawed, it doesn't necessarily follow that his final answer is exactly the reverse of what it should be.  The bottom line is I wouldn't want to give a clean bill of heath to TT system where there is reasonable suspicion that the earthing facility was showing signs of failing. As others have suggested, FI may well have been more appropriate than C2 - but both will give an unsatisfactory until more work is done anyway. If it's gone from 400Ω to 534Ω in the space of time between you both doing your respective tests, what's is lit likely to be in a month, at the end of the summer or next year? Can you really be reasonably sure it'll still be below 1667Ω? If not, how can anyone to state that the installation is satisfactory for continued service?

   - Andy.

He said he did not test the RCD trip times. He put >300ms on the report. My worst case trip time was 9ms. I don't think it's gone from 400 to 534. He loop tested it, I used a a long wire and a ground probe. I don't think it is unstable, but I will test it again after the weekend.

In his defence, Megger (and probably all the others) won't run the RCD test if the touch voltage will exceed 50V, which it would if he tried a 5x test (or auto).  What meter are you using, and what RCD tests did you do?  Is there a front end 100mA RCD, time delayed or otherwise? 

The touch voltage won't exceed 50 at 534Ohms @ 30ma. One of the tests I did measured the touch voltage at 13v @ 395 Ohms.

Megger CM500. All of the RCD tests, 1/2, I 0/180/, 5I 0/180 and ramp.