Complicated judicial arguments set to delay the effort to deport radical cleric to Jordan for at least 18 months

Government attempts to deport the radical cleric Abu Qatada face becoming embroiled in possibly years of legal argument, threatening to further embarrass the home secretary, Theresa May.

A panel of senior European judges will decide within the next three months if Qatada should be allowed to appeal to the grand chamber of the European court of human rights against his deportation.

The Home Office argues that it can deport him to Jordan, where he is wanted on terrorist charges, as the time frame for him to be protected against deportation ran out on April 16. His lawyers lodged an appeal the next day which they say fell within the time frame.

May says assurances from the Jordanian government that evidence obtained under torture will not be used against Qatada should allow his deportation to proceed. If the dispute is referred to the grand chamber, it would take 12-18 months before a decision on his status was reached, say legal experts.

Qatada's lawyers are understood to be considering options that would block May's efforts to deport a man once described by a Spanish judge as the "spiritual head of the mujahideen in Britain". They are thought to favour a twin-track approach that would see them seek to revoke the deportation order while preparing an appeal through the immigration courts if they are turned down.

If May were to then intervene in the process – by arguing that Qatada's case had no new merit – his lawyers would go on to seek a judicial review of her actions.

The complex dispute means he is unlikely to leave Britain for months. His legal team is expected to appeal for his release from a high-security unit in Belmarsh prison while it is resolved. They will also contest four aspects of his deportation, further complicating proceedings.

Qatada has spent the equivalent of a 20-year sentence behind bars without being charged. The team are expected to challenge this on the grounds of habeas corpus and say his treatment has been unreasonable.

They will argue that evidence produced under torture, and with possible financial inducements, would be used in his trial in Jordan. They claim that the fact that the case will be heard in a quasi-military court should be grounds for his deportation to be refused and will also say the government has not won the argument under article 6 of the European convention on human rights: that he can be guaranteed a fair trial.

Harry Fletcher, the assistant general secretary of the probation union Napo, said it was clear the protracted nature of the legal dispute meant Qatada would remain in the UK for some time.

"There are four major problems that need addressing by the Home Office before any deportation can be made," Fletcher said. "This will see the process take many months to resolve, if not longer."

Qatada's continued presence in Britain is an acute embarrassment for May, who has been accused of presiding over a shambles.

But the justice secretary, Kenneth Clarke, has dismissed the delay in deportation as "no big deal". Clarke said: "The key thing is when do we get the decision which we want, which is that he should be deported to Jordan to stand trial in a case where torture has not been used to get the evidence."