Such a regime is neutral in terms of competition as between second-hand motor vehicles imported from other Member States and similar domestic vehicles already registered in the Member State concerned and which have not been exempt from such a tax. Such neutrality exists where, first, such a system ensures that the amount of environmental stamp is reduced according to a reasonable approximation of the actual value of the vehicle, which it is for the referring court to verify and, second, that system results in the same tax burden on taxpayers who purchased a second-hand vehicle from another Member State and had registered that vehicle in the Member State which imposed the tax in question as the burden was for taxpayers who bought in the latter Member State a second-hand motor vehicle already registered in that Member State, for which it was necessary to carry out the first transfer of the right of ownership without benefitting from the exemption based on the payment of a previous tax, since that vehicle was, at the time of the levying of the environmental stamp duty, of the same type, characteristics and wear as the vehicle imported from another Member State.

Article 110 TFEU must be interpreted as not precluding a Member State from introducing a tax on motor vehicles which is levied on imported second-hand vehicles at the time of their first registration in that Member State and on vehicles already registered in that Member State at the time of the first transfer, within that Member State, of the ownership of those vehicles.

Article 110 TFEU must be interpreted as precluding a Member State exempting from a tax on motor vehicles which is levied on imported second-hand vehicles at the time of their first registration in that Member State and on vehicles already registered in that Member State at the time of the first transfer, within that Member State, of the ownership of those vehicles, the vehicles already registered and in respect of which a tax previously in force but found to be incompatible with EU law has been paid and not repaid.

A tax which is incompatible with EU law must be repaid with interest and its amount must therefore no longer be considered as being incorporated into the market value of the vehicles on which that tax is levied. Since the residual amount of the tax in the value of those vehicles is equal to zero, that amount is thus necessarily lower than the new tax, in the form of an environmental stamp duty, levied on imported second-hand vehicles of the same type, characteristics and wear. However, that residual amount of a tax ceases to be incorporated in the market value of a vehicle if the owner of that vehicle has, pursuant to EU law, the possibility of obtaining repayment of the tax, regardless of whether or not it was in fact repaid on the date of sale of that vehicle.

This mere possibility is likely to encourage owners of the second-hand vehicles from the Member State at issue to propose, in respect of those vehicles, even if the relevant tax has not been paid, a price which does not take that tax into account. If the tax has not yet been repaid, the buyers of such vehicles will be exempt from environmental stamp duty. However, the second-hand vehicles imported from another Member State will invariably be subject to environmental stamp duty at the time of the registration, in the Member State concerned, of the ownership of those vehicles. Thus, an exemption is liable to confer a competitive advantage on second-hand vehicles already present on the market of that Member State and therefore to discourage the importation of similar vehicles from other Member States.

(see paras 39, 41-43, operative part)