Rather than give you a top line figure that you then have to deduct your tax , National Insurance and pension to find out what your actually left with - Your employer is telling you if you do a days work for me this is what you will take home with you.
In any wage negotations I’ve ever had I always make it clear that I’m talking in a "after tax " senario ie "i want £180 a day after tax and national insurance . From that £180 the only thing left to deduct is my pension . It keeps them from giving you what looks like a good rate but then you lose out when your tax and \national Insurance is deducted . Its up to them to sort out your tax and N.I (and possibly pension )