MCB RCD Problem

[Flying Sparks]

I could do with some help / guidance.
Last week I fitted a new CU into an old cottage. The house was rewired approx 30 years ago.
The Ring Final Circuits r2(2.01) was much higher than rn(0.38) & r1(0.43). 6mm & cpc 2.5mm
When I did the Continuity test I found the R1 + R2 was 2.27.
The Insulation Resistance was lower on this system ( 255 M ohm) - other systems normal.
When I plug anything into the the Ring Main it trips both the RCDs and the MCB for the Ring Main only.
Any suggestions?
Thanks

 

[Flying Sparks]

That was the only thing I changed & it worked. Tested OK.
I don't know why the MCB tripped.