But that has been the policy in France, and the rest of mainland Europe, for decades before it became policy in the UK.
The differential between diesel & petrol in the UK used to be that diesel was maybe a penny or 2 more, now it is up to 10p more expensive.
You are right, if I'm not mistaken in France it was a policy from the 80s. My point is that it was a french policy that artificially made diesel more competitive than petrol, the recent narratives are that diesel is now surtaxed or that the EU was the source. In reality, the main reason was that french car manufacturers, mainly PSA, were particularly good with diesel engines, so they lobbied for an advantageous fiscal policy for diesel.