hmrc.gov.uk used to accept passwords up to 15 characters long. GOV.UK only accepts passwords up to 12 characters long. If you input a password of 13-15 characters into GOV.UK it won't let you log in. You can't change a password until you have logged in. Fortunately there's a simple work round - just input the first 12 characters! GOV.UK accepts this. This problem won't affect many users because most have passwords of less than 13 characters.
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