We applied from the UK last August. Our case seems to be taking a longer than the listed processing times (7 months so far since we submitted, 5 months since London started processing it). They haven't contacted us to request an interview or for more information, and e-cas said they had my medical results in December, so not sure why it's taking so long. I'm originally from Australia, so all I can think of is they're waiting on something from Australia. But who knows. We've ordered our CAIPS notes to try and get an idea of what's happening.
The good news for you though, is London appears to be one of the quicker visa offices at the moment. Take a look at
http://www.cic.gc.ca/english/information/times/international/05-fc-spouses.asp for the processing times during 2008. The 2007 processing times were slower, so they seem to be improving considerably.
Also, check out Trackitt if you haven't already and add your case there once you submit it (trackitt.com/canada-immigration-trackers/family-class). You can filter by Visa Office (select London) and Family Program (select Spouses & Partners) to see the current timelines for cases being processed in London.