Good point . I had a word about this with the guy who MOT'd mine recently, he was obviously aware of all the changes to the MOT regs but described this as a "grey area". What he told me was that he would fail a car that had them fitted if they didn't work, he also said that if they were completely removed then he would find it difficult to fail them as at that time he didn't have a list of cars that had these fitted, in other words if he spots the washer bottles, pipes, brackets, etc still in situ then it'll be a fail. That's only one tester though, others may well see it differently. If you buy a UK Zed with an aftermarket front bumper then its well worth checking that the parts needed to get the washers working are present or available as it may not always be a grey area.
Pete