Can I get a court order to stop someone doing something urgently?

Yes, you can apply to the High Court for an interim injunction, which is a temporary order preventing certain conduct until the full dispute is heard. In urgent cases you can apply without notice to the other party, though the court will expect you to put all relevant facts before it fairly. The court considers whether there is a serious question to be tried, where the balance of convenience lies and whether damages would be an adequate remedy, as well as the overall justice of the case. You will usually need to give an undertaking as to damages, promising to compensate the other side if the injunction is later found to have been unjustified. Gather evidence such as emails and file access logs and ask a lawyer to prepare affidavits.