Judges in the Netherlands have refused to send a suspected drug smuggler back to the UK because of concerns that conditions in British jails are inhumane.

An initial application to extradite the unnamed man, who had been on the run for two years, was refused this week due to the reported state of HMP Liverpool where he would probably be sent.

The court of Amsterdam heard how inspectors had found “some of the most disturbing prison conditions we have ever seen” and “conditions which have no place in an advanced nation in the 21st century”, in reference to report on the state of prisons in the UK published last July.

A surprise inspection of HMP Liverpool in September 2017 found it was infested with rats and that inmates lived in squalid conditions, afraid of being attacked because of increasing violence. Similar conditions were found in HMP Birmingham and HMP Bedford.

The Dutch judges said on Wednesday they were concerned the man, who was wanted in relation to cocaine and heroin smuggling on Merseyside, was at “real risk of inhuman or degrading treatment” if returned.

The man had been made the subject of a European arrest warrant at Liverpool magistrates court in July 2017.

His lawyer argued that the extradition should be refused based on the prison inspectors’ reports.

“The UK judicial authorities state that British prisons are doing quite well, but the circumstances discussed in the reports are still the same as before, even though more staff may have been appointed,” the lawyer said, according to documents first reported by the Liverpool Echo.

“The situation is still not good and the letter of 24 April 2019 [from the director general of prisons] gives no assurance that the situation is now different from before. Nor is there a guarantee that the person claimed will not be placed in HMP Bedford, HMP Birmingham or HMP Liverpool after surrender.”

Citing article three of the European convention on human rights, the Dutch judges said they did not have sufficient evidence that the man would not be returned to such conditions.

They told the court: “What has been put forward by the UK judicial authorities is too general and insufficient to assume that the detention conditions in the aforementioned prison institutions have significantly improved.

“In these circumstances, the expectation that the situation will improve rapidly is not sufficient to assume that the real risk of inhumane treatment has actually disappeared. The already established real danger of inhuman or degrading treatment in these establishments has not been eliminated.”

The court said it would delay its final decision on the extradition “until it obtains additional information on the basis of which it can rule out the existence of such a hazard”.

A letter written by the director general of prisons to the court insisted that steps had been taken to improve the jails. “We do not accept those conditions anywhere in our prisons amount to inhuman or degrading treatment contrary to article three,” the letter said.

A UK government spokesman said overcrowding was being reduced and that new governors had been appointed at the three jails.