The European Court of Human Rights has sanctioned the extradition of five terror suspects, including radical Muslim cleric Abu Hamza al-Masri, from the UK to the US.
How does extradition between the two countries work?
Extradition between the United States and the UK is set out in a 2003 treaty, which later became part of domestic law in both countries.
Extradition from the US to the UK
When the UK sends an extradition request to the US, it is received by the US State Department via the British Embassy in Washington.
A State Department lawyer looks at the request and assesses whether it conforms to the 2003 Treaty that underpins extradition between the two states.
A critical test set out in the treaty is that the British request must include "such information as would provide a reasonable basis to believe that the person sought committed the offence for which extradition is requested."
This requirement does not apply to requests submitted by the US to the UK.
The Department of Justice also examines whether there is "probable cause" to justify the request.
This test comes from the Fourth Amendment to the US Constitution which states that people cannot be arrested unless the authorities have "probable cause" for their action.
So, once a suspect has been arrested, they can challenge the lawfulness of the request.
If the request is ruled lawful, the Secretary of State takes the final decision after considering human rights issues - such as whether the suspect could be denied a fair trial or face inhumane treatment.
A Home Office-commissioned independent review, which concluded in October, found the US had not refused any extradition requests since the treaty came into force. A total of seven US requests were refused by the UK in that time.
Extradition from the UK to US
The process begins when a US prosecutor obtains an arrest warrant with the approval of the domestic courts.
In England and Wales, the Crown Prosecution Service acts on behalf of the US in taking the case through the courts.
Once the police have arrested the suspect, the courts must decide whether or not the US has met the tests required for an extradition to take place. This is a fairly technical hearing in which the lawfulness of the request is examined.
The US does not need to provide all the evidence in a case, as if the allegations were being tested in a full trial by British judges.
What this comes down to is proving to the courts that there is reasonable suspicion - essentially the hurdle police need to jump to justify an arrest - but obviously short of what is necessary to get a conviction.
Are the tests the same?
The 2003 Act effectively made it easier for the US to seek the extradition of someone from the UK because the US would no longer need to provide a "prima facie" case to British courts - proving your case on the face of available evidence.
Campaigners say this is unjust because someone can be extradited without the case being properly tested. But supporters of the treaty and the related British 2003 Act argue that the removal of the prima facie test simply means that suspects face the same broad test in each country.
The Home Office's extradition review, led by former Court of Appeal judge Sir Scott Baker, argued there was no real difference between the US tests of "probable cause" and the introduction of "reasonable suspicion".
The panel said that both tests amounted to the basic standard of proof used by police officers in both countries to make an arrest.
But critics say that's a red herring. Campaign group Friends Extradited says the real issue of imbalance is that while the US courts don't allow an extradition until a judge has examined the quality of the evidence, because of the constitutional rights of the suspect, a British judge is merely examining the quality of the application - not the case the individual faces on arrival in the US.
The Commons Home Affairs Select Committee said British people were losing confidence in the UK's extradition arrangements with the US and major changes were needed "to restore public faith".
Parliament's Joint Committee on Human Rights said in its June 2011 report on extradition that the burden of proof for extradition should be increased - but the US argues that it cannot ask the UK to hand over a suspect unless its request has already met the same test in its own courts.