The Carnets in London are OK, like you say. That's the ones I meant
when I wrote:

Paris 5.30 / 1.40 / 1.05
London 6.45 / 3 / 2.25

(ie the E2.25 being £1.50). The problem is the ratio: 2.25 is more
than a 1/3 of the travelcard price (E6.45), while in Paris, the E1.05
fare is less than 1/5 of the E5.30 travelcard.