I work as a Mid Product Designer for a big company ($8+ billions) in London (UX/UI, not Industrial design). My salary is currently £45k, which I now realise it's too low. It's a temp contract for now though. This contract will last until the end of this year and then they want to convert it to perm.My manager etc. already agreed that I should go perm, so right now it's just a matter of bureaucracy and I'm waiting for an official offer.I think I should definitely ask for a raise when that time comes. I'm now fully integrated with how the team works. I handle big projects that are extremely profitable for the company. Everyone likes me. And if they had to find someone else, it'd require them a lot of money and resources to do that. One of our senior designers told me it was a nightmare last time around, because they couldn't find anyone good, so he thinks I've a lot of leverage at this point.Also, my skills are now very different compared to when I accepted my previous contract many months ago. I improved a lot and I'm worth more.My idea is to lay down the things I'm bringing to this company, and then say something like "...because of this, I'd like to have a competitive market rate. Mid Product Designers in London earn £58-60k. I'm flexible and willing to find some common ground".Any advice on this? Did any of you negotiate their salary when going from temp to perm? (I'm not a contractor, I've a normal temp contract and I've a yearly salary)