Concerns have been raised over a "serious defect" in the NHS Covid app.
Currently coronavirus passports can be downloaded from the official NHS Covid app but concerns have been raised about information displaying booster jabs.
As more and more international borders open up, different countries require different levels of immunisation to travel.
For some, they require a coronavirus jab within the last six months after fears the strength of the vaccination begins to wane.
So the booster jab could, for many Britons, be their lifeline if they wish to jet off abroad.
But the House of Lords has now raised concerns the information is "hidden away" on the mobile platform and not prominently displayed, as earlier doses were.
It came as the Prime Minister Boris Johnson stressed the importance of booster vaccines in dealing with the pandemic as the UK goes into winter.
The NHS has opened bookings for people who are five months after their second dose so they can have a booster at the six-month point.
Highlighting an issue with the app during an update on vaccinations in the upper chamber, leading lawyer and independent crossbencher Lord Pannick said: “Can the minister explain why the valuable NHS app does not prominently display that the individual has received a booster jab as is the case with the first two doses?
“The information is hidden away on the app and it cannot be downloaded.
“This is a serious defect because some foreign countries… now require proof of a jab in the past six months, given the waning effect of earlier doses.
“And there are many domestic contexts where the ability easily to prove that you have had a booster dose would be valuable.”
Responding, Tory frontbencher Lord Kamall said he was made aware of the issue by a number of peers and had raised it with NHSX, which oversees the app.
He told the peer: “They said they are looking into it and trying to work on a fix as soon as possible.”
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