can we argue for payment of one PCN rather than two?
Of course you can, basically on the basis of a disproportionate penalty for a simple mistake of navigation in London. However you will be arguing in mitigation as each PCN is for a different location.
That's my view, others may differ. In addition, there may well be a 'technical'defence based on the council's management of the enforcement process. One of our experts on here is expert at finding holes in their armour plate, or even punching through it !!