A High Court judge asked to rule on a passport dispute between Home Secretary Theresa May and a 45-year-old woman who was born in India has described the conduct of the UK Government as "grotesque".
Mr Justice Walker said the "stance taken on behalf of the Home Secretary" during the case could not be described as "honourable".
The judge said "untenable objections" had been made against Deelavathi Bondada's claim to British citizenship.
He today concluded that Ms Bondada - whose application for a passport had been rejected - was a "British citizen by descent".
And he made complaints in a written ruling on the case following a High Court hearing in London.
Mr Justice Walker said the "central question" he had to decide was whether Ms Bondada was a British citizen by descent.
The judge said he had no doubt that the question had to be answered in Ms Bondada's favour.
He said he had examined objections to Ms Bondada's claim raised by UK Government officials.
"The stance taken on behalf of the Home Secretary ... is a stance which cannot be described as honourable," said Mr Justice Walker.
"Untenable objections were taken to (Ms Bondada's) claim.
"The stance taken in those objections refused to engage with compelling DNA evidence.
"The result was that this stance effectively made an accusation that (Ms Bondada's) mother has lied about the patronage of her children for more than 60 years.
"At a very late stage in the present proceedings the Home Secretary accepted the DNA evidence.
"Nevertheless the stance taken on behalf of the Home Secretary when rejecting (Ms Bondada's) claim has, without a shred of evidence to support it, continued to make the same effective accusation."
He added: "The conduct of the UK Government in this regard has been grotesque."
The judge said he did not criticise lawyers who represented ministers - he said they had been seeking to "defend an impossible position".
He said Ms Bondada's family said she had been born in the village of Nagullanka near Chennai.
And he said he had analysed "crucial issues" about her date of birth and her parents' marital status before concluding that a decision to refuse her a passport should be quashed.