Mark Fleming said:

The chargers themselves only require 3 phase & earth

So there is no neutral to lose.

note that no neutral does not always mean all 3 line currents are balanced, you can have a delta of 3 different resistances,  3 different line currents, and no neutral current, so if the PEN goes O/C there is no ground pull.

Mike.

Chris Pearson said:

So there is no neutral to lose.

Not quite - the Neutral may be there to provide the PE at the service head.

However, in this case, OP has confirmed they are likely to use the N of the TPN for small single-phase loads at least (anti-condensation heaters)

Yes, I noticed that, but if it isn't part of the charger, does it matter?

Is that likely within the chargers themselves? My first thought was that by no means all cars can draw 3 phases, but then I realised that the chargers are DC so unless they became faulty, how would an imbalance arise?

Chris Pearson said:

Yes, I noticed that, but if it isn't part of the charger, does it matter?

Yes, the demand that produces the neutral current is based on the phase balance of the whole installation as defined in BS 7671. How you define what the extent of the installation is based on the definition of that term in BS 7671 is another question.

Chris Pearson said:

DC so unless they became faulty, how would an imbalance arise

Agreed - but just be a little careful here as some 'DC chargers' are combined Mode 3 and Mode 4, and can switch either single-phase or three-phase AC (as the car demands) in Mode 3 to a vehicle that is not capable of Mode 4 (DC only) charging.

What a minefield!

What a minefield!

But these have no neutral connection, so the most disruptive thing they can do is to have unequal phase currents that  sum to zero. (en extreme example is a load L1-L2 and nothing on L3)
In many ways car charging is a simple thing made complex.
Cars should have been earth free / class 2 or inductive as actually some very early examples were, but it has fallen by the wayside in favour of copper connections, and then of course we fall over the various national attitudes to earthing, and neutrals and 3 phases being a domestic supply or not. Once electric cars meet the more liberal parts of the world the preferred connector will be 2 core cables and wing nuts or croc clips, and a box to kid the car it is a legit supply.
Mike