Just to confirm previous posts best way to get 18 digit Ref is via the web chat. Type Advisor and you get a real person. I already had a forecast (that took 14 months!) so process was very slick. Got the 18 digit code within minutes (suggest you copy and paste it somewhere) and then paid from Bank Account via HMRC web page. Whole thing from typing "Advisor" to completing payment and getting confirmation email took less than 20 minutes.