More than 70 MPs have signed a letter urging the home secretary to ensure Julian Assange faces authorities in Sweden if they request his extradition.
The WikiLeaks founder, who is now in UK custody, was arrested on Thursday after years in Ecuador’s London embassy.
Sweden is considering whether to reopen an investigation into rape and sexual assault allegations against him.
And the US is seeking his extradition in relation to one of the largest ever leaks of government secrets, in 2010.
Assange sought refuge in the Ecuadorian embassy in 2012 to avoid extradition to Sweden over allegations of sexual assault, which he has denied.
At the time, the Australian-born 47-year-old said he had had entirely consensual sex with two women while on a trip to Stockholm, and that the Swedish claims against him were part of a smear campaign.
Swedish prosecutors dropped a rape investigation into Assange in 2017 because they were unable to formally notify him of the allegations while he stayed in the embassy.
Two other charges of molestation and unlawful coercion had to be dropped in 2015 because time had run out.
But Swedish prosecutors say they are now re-examining Assange’s case at the request of the lawyer acting for the alleged rape victim.
In their letter to Sajid Javid, 70 parliamentarians – chiefly Labour MPs – urged the home secretary to “stand with the victims of sexual violence” and ensure the rape claim against the WikiLeaks founder can be “properly investigated”.
“We do not presume guilt, of course, but we believe due process should be followed and the complainant should see justice be done,” it says.
Labour’s Stella Creasy tweeted a copy of the note sent to Sajid Javid.
On Friday evening, shadow foreign secretary Emily Thornberry said he should be extradited to Sweden before any attempt to get him to the US. She said she was “disgusted” the American allegation had been “allowed to eclipse” the sex offence case.
Assange was dramatically arrested by UK police on Thursday after Ecuador abruptly withdrew its asylum.
Westminster Magistrates’ Court found him guilty of a charge of breaching bail later that day. He faces up to 12 months in prison for that conviction.
The MPs’ letter says both UK and US authorities seem to have been aware in advance of Ecuador’s decision to rescind Mr Assange’s political asylum, but said it was a matter of “grave concern” that Swedish authorities did not appear to be aware of the impending arrest.
On Friday, Labour leader Jeremy Corbyn said the UK government should not extradite Julian Assange to the US.
The United States alleges that Assange conspired with former US Army intelligence analyst Chelsea Manning to access classified information on Department of Defense computers.
Documents published by WikiLeaks relating to the war in Afghanistan revealed how the US military had killed hundreds of civilians in unreported incidents.
The US has already charged the 47-year-old with a single count of participating in the hacking of intelligence computers to reveal controversial intelligence operations in the United States.
If found guilty, Assange could be jailed for up to five years.
Extradition proceedings are dealt with by the courts.
According to the Home Office, the home secretary can bring a limited number of factors into consideration when deciding whether to order a person’s extradition.
These include whether the person might be at risk of the death penalty or whether the requesting state might try to add additional charges it has not specified.
However, lawyer Rebecca Niblock said that, if Sweden made an extradition request, it would be for the home secretary to decide which would take precedence, considering factors such as which was made first and the seriousness of the offence.
The rape allegation in Sweden has a limitation period which expires in August 2020; inquiries into claims of molestation and unlawful coercion have already been timed out.
Assange is due to face a hearing over his possible extradition to the US on 2 May.
His lawyer, Jennifer Robinson, said they would be fighting the extradition request. She said it set a “dangerous precedent” for journalists publishing information about the US.
The UN has called for his right to a fair trial to be respected during any extradition process.