From the regs: “A car with HID lights MAY also have headlight washers and self levelling which must be checked and in working order if fitted.”
It doesn't say "MUST" and therefore if they're not fitted, cannot be tested and are not a requirement, any more than a spare wheel or reversing lights are.
Also, from the AA:
"HID headlights can cause dazzle if they are dirty or aimed too high, so they are generally (if light output exceeds 2000 lumens) fitted in conjunction with headlamp cleaning and levelling systems. Where HID or LED dipped beam headlamps are fitted the tester will switch on the headlamps and check the operation of any headlamp levelling and cleaning devices fitted. The car will fail if a headlamp levelling or cleaning device is inoperative or otherwise obviously defective."
You still hear stories of people being failed for having them though, but I'm not sure if that's because the car was presented dirty, the lights were badly aligned, the tester was over-zealous, or they misinterpreted the regs.