Mines failed it’s MOT under the pre-May 20th regs for the headlight washers being inoperable. I’m under the same impression as you
@Davyy that new regs meant headlight washers were now only a test requirement after 2009, but I could well be misunderstanding the new rules (that said, I don’t know if they would still fall under the old “if fitted, must work” type mantra).
In the end my issue turned out to be that the lines were clogged with crud and dirt as one of the previous owners had looped the supply lines from the washer bottle, due to the age old problem of the jets themselves leaking, then when I reconnected the washers up, all the crap in the lines just stopped the fluid getting thro. Could be worth a check, if your MOT tester is adamant on them working before issuing a certificate.