This is not a tax, it relates to Heathrow’s other regulated charges, and is outside the remit of the CAA. As the value of the charge is subject to a commercial agreement between Heathrow and the airlines that use the airport, we suggest your refer you query to Heathrow in the first instance.

You mentioned that this is not a tax, but both British Airways and Swiss (for example), are categorising it as such.
Are you saying it should not come under the “tax” section of an airline ticket and should come under the “airline imposed surcharges” section, along with items like the fuel surcharge?
Are you also saying that this tax not regulated by yourselves?
If it is not regulated by yourselves, what is to stop Heathrow doubling or tripling this to make up for a reduced income from the PSC?

Taxes can only be imposed by the government, this is a charge that Heathrow is placing on all departing passengers. I understand they have a statement on this and a document on their website that goes into some detail about the charge. I think it is more appropriate that you speak to them.