Interesting question.

Personally I would say a C2 on the EICR.  As you state 2 CU/DB in close proximity with the OFF in different positions which COULD cause confusion at the best of times but consider the confusion during an emergency, in turn you are heighlighting a possible risk.

My understanding of a C2 on an EICR means that something on your installation is POTENTIONALLY dangerous

Think about Hierarchy of Controls


    Elimination
    Substitution
    Engineering controls
    Administrative controls
    Personal protective equipment (PPE)

By adding a robust label for the ON and OFF  for BOTH CU/DB you could drop this down to a C3, the caveat here is you are altering the original design and spec of the Iso.  Eg the unit may become warm and your label could fall off or could potentially cause a fire risk.  Further worth noting the age of the isolators and if they are double or 4 pole in the case of 3P&N so the C3 could recommend the isolator be upgraded in time to the current spec of BS7671

Reg 462.2 Isolation of all LIVE conductors (so L and N)

It would be interesting if you could add some pictures of the DBs. 

Reg 462.2 Isolation of all LIVE conductors (so L and N)

except as detailed in 461.2 - so for TN systems generally, isolation of N is NOT required (other than for the main switch of single-phase domestics).

   - Andy.

Reg 462.2 Isolation of all LIVE conductors (so L and N)

except as detailed in 461.2 - so for TN systems generally, isolation of N is NOT required (other than for the main switch of single-phase domestics).

   - Andy.