An illegal immigrant who was charged with sexually molesting a woman within days of his smuggle into Britain has reportedly been blocking attempts by the authorities to deport him by claiming he is a Syrian refugee.

Abdulrahman Abunasir filed an asylum claim while being held at an immigration detention facility and serving an 18-month sentence for the sexual assault, according to the Daily Express.

But the report said the language tests given to Abunasir showed that he failed to answer basic questions about his supposed homeland, Syria. Experts said he might have come from Egypt. But authorities have been unable to deport him because they are also not certain if he is really Egyptian.

Abunasir was previous detained in France where he claimed to be a Palestinian.

The case of Abunasir worries British authorities and citizens because it is now almost impossible to deport foreign criminals due to overbearing human rights laws, said the Express.

"He cannot be deported because there is no way of determining with 100 percent certainty that he does not come from Syria, which is being torn apart by a brutal civil war,'' said the report.

On the one hand, the British government is apparently not interested in keeping him any longer in the detention centre because it is costing British taxpayers £40,000 a year per inmate to maintain.

Abunasir has been at the centre for two years with the bill for his incarceration already topping £80,000. Prior to this, he served nine months in jail for attacking a young woman in 2013, according to the Express.

"Taxpayers will be incensed if foreign criminals are using the desperate refugee crisis to try and avoid deportation,'' according to Jonathan Isaby, chief executive of the TaxPayers' Alliance.

"On the whole, the system for removing offenders must be dramatically improved. It's not right that British taxpayers are picking up the tab for foreign criminals to stay here."

Critics, meanwhile, said the case that "made a mockery of the British judicial system' indicates the need for the government to improve its policy on deportation of foreign criminals.

"It's regrettable that a sex offender who has committed a very serious offence cannot be removed. As long as this case continues, there is a high cost to the taxpayer," said Lord Alex Carlile QC, the former anti-terrorism laws reviewer.

"Foreign nationals who abuse our hospitality by committing crimes in the UK should be in no doubt of our determination to deport them,'' said a Home Office spokesman, according to the Express.