SCREENGRAB/BBC
The restrictions mean diplomats are banned from travelling 60km outside London without permission.
The Home Office said this mirrored restrictions on British officials in Eritrea's capital Asmara.
In the 12 months to June only seven people from Eritrea were returned there from the UK, according to Home Office figures. A further 244 Eritreans were returned to other countries.
Over the same period, more than 5,800 Eritreans arrived in the UK via small boats. A further 1,300 were given visas, mostly to join people already settled in the UK.
Dr Madeleine Sumption, director of the Migration Observatory at the University of Oxford, said targeting Eritrea would have little impact.
"Eritrea is one of the major countries of origin for asylum seekers coming to the UK - we had roughly 7,000 asylum applications in the last year of data, roughly 8% of the total," she told BBC Radio 4's Today programme.
"Most Eritreans who come and claim asylum are not removable at all - the government would never be in negotiations to remove them because 84% are successful at initial decision; more will be successful on appeal."
She added that about 1,400 people were initially refused asylum, but that this number would reduce after appeals.
Many young Eritreans try to leave the country - which is a one-party state - to avoid military conscription, which can last for decades.
Eritrea has never held an election since independence from Ethiopia in 1993 and there is no independent media. Critics of President Isaias Afwerki have been arrested and jailed for many years, often without trial.
Only four religions are permitted in the country – Orthodox Christianity, Sunni Islam, the Roman Catholic Church, and the Evangelical-Lutheran church of Eritrea – and followers of other religions have been locked up for years on end.
Last November, the Home Office said it was prepared to suspend visas from countries that "fail to co-operate with the return of their citizens".
Earlier this year, the UK threatened visa restrictions against Angola, Namibia and the Democratic Republic of Congo (DRC).
Restrictions were announced against the DRC last year, but the Home Office said these have been lifted after co-operation on returns improved.
Angola and Namibia both agreed changes before restrictions were introduced.
But Sumption pointed out that the government may avoid targeting certain countries to avoid damaging trade relationships.
"If you're looking at overall numbers of people who are refused asylum and not returned to their country of origin, it would be places like Pakistan, also Bangladesh that are right at the top of the list," she said.
"But the collateral damage of a ban on visas for those countries when you have so many international students coming, for example, [and] a lot of people coming on work visas would be much greater than a country like Eritrea."
According to Home Office data, more than 20,400 people have arrived in the UK by small boats so far since the beginning of this year, down 40% from the same period last year.
There were more than 40,600 returns and deportations from the UK from July 2025 to June this year - an 8% increase on the same period last year.
Of those who had been returned, fewer than 6,000 have been convicted of a criminal offence.