A Home Office error has led to delays in passport renewals for more than 1,000 UK-born children of parents from eight EU countries.
It came after an error in guidance in 2008, which was corrected in 2014, meant some families from the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Slovakia and Slovenia "had difficulty renewing passports for their children", the Home Office said.
Some EU citizens were told they did not have the documentation required to prove their children were entitled to British passports, despite them already having been issued passports.
A spokesman said it regrets "any inconvenience or delay" that has been caused, and added: "We want there to be no doubt - if you are settled in the UK legally, any child you have in this country thereafter is British."
'Error in guidance'
Problems arose after the initial guidance did not ask for full documentation when passports were applied for. It meant a number of passports were issued without officials seeing the required evidence of permanent residence in the UK.
Changes to the system have since allowed for some discretion if an application to register a child as a British citizen is lacking some evidence.
It is believed that since these new measures were put in place to resolve the issue, more than 1,000 cases have been referred to UK Visas and Immigration (UKVI), a division of the Home Office, and none have been refused.
The Home Office spokesman said: "An error in guidance issued in 2008, which has since been corrected, meant that some EEA (European Economic Area) citizens have had difficulty renewing passports for their children. We regret any inconvenience or delay that this has caused.
"In response, we have set up a support function in Her Majesty's Passport Office to identify renewal applications from the affected group and, where appropriate, support them to first register their child as a British citizen.
"This process does not require the same evidence as a passport renewal, and the Home Office bears the cost. Once that registration process is complete the child is able to make a new passport application."