If your file has been transferred to Mississauga, that's a great thing actually. Mississauga is know to be one of the fastest processing offices. Most simple applications are finalised there within a month to three. So that's a very good sign. London Visa Office is one of the slowest in processing. They have a huge backlog and it might take about 6 - 12 months before you hear anything from them. However, there have been a few cases of applications first transferred to Mississauga and then forwarded to other offices for further processing (especially if they find something off in the application or to help the PA's visa office reduce its backlog). Whatever your case is, Mississauga transfer is generally a good thing. Congrats!