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.
The whistle-blowing website Wikileaks has published thousands of classified documents covering everything from the film industry to national security and war.
The Swedish case
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 both Sajid Javid, 70 parliamentarians - chiefly Labour MPs - urged them to "stand with the victims of sexual violence" and ensure the rape claim against the Wikileaks founder could 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.