Basically, London don't want to hear from you until after 6 months has passed from when London start processing your application. If your case is straightforward, London seem to be fairly quick these days at processing an application and it might only take a couple of months (consider yourself lucky if it does!) from the date they start processing it.
If it's not straightforward (i.e. need an interview, documents missing, need more info, or from what I recently found out about mine - need a background security check), it could drag on for months. We waited the full six months and then my wife got her MP's office in Canada to make an enquiry for us today.
So basically, after only waiting six weeks, you're still well inside the published processing timelines. The current timelines for London have 30% of cases processed in 2 months, 50% in 3 months and 70% in 5 months.
See
http://www.cic.gc.ca/english/information/times/international/05-fc-spouses.asp for more details, and keep in mind the time starts from when London started procesisng it.