Two people were jailed on Friday for subjecting feminist campaigner Caroline Criado-Perez to abuse on Twitter.

Isabella Sorley was jailed for 12 weeks at Westminster magistrates' court. Co-defendant John Nimmo was jailed for eight weeks.

Judge Howard Riddle said it was "hard to imagine more extreme threats".

He said that, despite the defendants' claims, the harm threatened against Criado-Perez "must have been intended to be very high".

Nimmo also targeted his abuse at Stella Creasy, the Labour MP for Walthamstow, with the message: "The things I cud do to u [smiley face]", and: "Dumb blond bitch".

The judge said the effect of the abuse on Criado-Perez had been "life-changing".

She described "panic and fear and horror", he said.

He added that the abuse had also had a substantial impact on Creasy, who had had a panic button installed in her home.

The judge said of the abusive tweets: "The fact that they were anonymous heightened the fear. The victims had no way of knowing how dangerous the people making the threats were, whether they had just come out of prison, or how to recognise and avoid them if they came across them in public."

Criado-Perez tweeted her response following the sentencing: "It's hard to get my thoughts together at the moment as my stomach is churning – hearing the outcome has made me realise how tense and anxious I have been feeling.

"I did not attend the sentencing as I didn't feel I could cope with being in court with them, and I didn't feel sure that the judge would understand how terrifying and scarring the whole experience has been for me, which again is not something I could face. I feel immensely relieved that the judge clearly has understood the severity of the impact this abuse has had on me.

"The damages that have been awarded to me will be going to charity. When this has all sunk in I will decide which charity."

Sorley and Nimmo were each ordered to pay £800 compensation.

The court heard that university-educated Sorley has 25 previous convictions, the majority for being drunk and disorderly.

While on bail for this case, she also committed two offences of assaulting a police officer and is awaiting sentence for an assault on New Year's Day, the court heard.

During mitigation, Sean Caulfield, defending Sorley, said she was a victim of new technology as she did not understand the impact of what she was doing.

"She understands what it must have been like now. At the time, it seems, she did not," Caulfield said.

"Maybe there's an issue about the technology and Twitter and people understanding what it must be like on the other end.

"She is a victim of that, if nothing else – a victim of a lack of understanding of what this new technology can do and how powerful it is."

Paul Kennedy, representing Nimmo, described him as a "somewhat sad individual" who is "effectively a social recluse".

Kennedy said that, when Nimmo's original tweet was responded to and retweeted, it encouraged him to send more messages as he saw it as an "indication of popularity".

"He said that if that had not happened then he would not have pursued this course of action.

"He believed at that time that there was a conversation and he was engaging in that conversation."

Kennedy said Nimmo had no particular opinion on Criado-Perez's campaign for a female figure to appear on a Bank of England note, but had seen the topic trending on Twitter and his lack of experience of social interaction meant he did not know his behaviour was inappropriate.

Sorley, 23, used Twitter to tell Criado-Perez to "f*** off and die you worthless piece of crap" and "go kill yourself", and said: "Rape is the last of your worries."

Nimmo, 25, told Criado-Perez to "shut up bitch" and "Ya not that gd looking to rape u be fine", followed by: "I will find you [smiley face]" and then the message "rape her nice ass", Westminster magistrates court heard.

Nimmo, from South Shields, Tyne and Wear, and Sorley, from Newcastle-upon-Tyne, pleaded guilty to sending menacing tweets on 7 January, admitting they were among the users of 86 separate Twitter accounts from which Criado-Perez had received abusive messages.

A 32-year-old man remains on bail as part of the investigation, a Metropolitan police spokesperson said.