Hi Natalia
Assuming these are not to be classed as direct expenses as we do not know what your client does - then I would suggest 7606. Or set up your own if you want to split them to monitor them (in the 76xx region) - as long as you are consistent.
Assuming the Director's own car is being used and you have a way of being able to show HMRC if required that you are logging mileage (spreadsheet or paper log) then run through motoring expenses nominal (and DLA if not physically paid).
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Joanne
Winner of Bookkeeper of the Year 2015, 2016 & 2017
Thoughts are my own/not to be regarded as official advice,which should be sought from a suitably qualified Accountant.
You should check out answers with reference to the legal position