no. you can say you want to drop the charges, but the police/cps do not have to listen to you and can choose to prosecute anyway (and usually do if injuries are severe enough/a particular offence is committed/done by a repeat offender). if you say something like i didn't mean it/i exaggerated, they can prosecute you for perjury (lying) or wasting police time. even if you withdraw a statement they can still make you appear in court, and if you choose to say nothing when you are there you can be done for contempt. you cannot petition to lower the level of charges, only say in court you do not want them to go to jail - but that is completely up to the judge sentencing, and they rarely listen and make their own mind up as to the punishment people get. your partner needs to think very, very carefully about what he does and take advice from his solicitor......and if somebody stabs someone (irrespective of who they are and how they are related to you) then they should be put on trial and punished, imho, as they are a dangerous individual. what if he does it again and the next person is not so lucky? the police, cps and the judge basically get to decide what happens after a crime is reported......and i think it is a good thing that relatives/friends do not interfere in this process. if your sister or her bf is putting pressure on you or your bf.....this can also be seen as interfering with a witness, which is also an offence and is taken very seriously as it interferes with the judicial process. the person in question is in very deep doo doo indeed.