But you have to realise that a) some of those articles are written by estate agents so while I'm not saying they are lying, they will exaggerate rental price 'drops' in order to draw in business! b) none of those drops are substantial. In late 2008, you could haggle down your rent maybe £20-50/month (on average) from the original asking price, but that's not really 'rents falling' and is extremely subjective and dependent on the demand in the area. You can always still haggle at any time any year, but it's a matter of what landlords are willing to accept in the market. Hubby says most places are going for their asking price in his area, though not up to 2007 levels of people actually having to bid OVER the asking price to secure a place!
Sorry, I hope this makes sense. The rental market in London is so strong (and always will be) that any shift will be negligible.