Have a look in /wp-content/plugins/wp-super-cache/wp-cache-phase1.php you will find it there

Hi Iris

Sorry about the slow reply been very busy - 3600 is seconds which is the equivalent to an hour so it should be fine with this new value.

In terms of rel=canonical that will pass value the same as a 301 redirect - for evidence have a look here:

http://moz.com/learn/seo/canonicalization

"Another option for dealing with duplicate content is to utilize the rel=canonical tag. The rel=canonical tag passes the same amount of link juice (ranking power) as a 301 redirect, and often takes much less development time to implement."

See DR Pete's response in this Moz Q&A:

http://moz.com/community/q/do-canonical-tags-pass-all-of-the-link-juice-onto-the-url-they-point-to

http://googlewebmastercentral.blogspot.co.uk/2009/02/specify-your-canonical.html

https://support.google.com/webmasters/answer/139066?rd=1

http://searchenginewatch.com/sew/how-to/2288690/how-and-when-to-use-301-redirects-vs-canonical

Matts Cutts stated there is not a whole lot of difference between the 301 and the canonical - they will both lose "just a tiny little amount bit, not very much at all" of credit from the referring page.

I would definitely say that your site is over-optimised and that you are having issues as you have built a lot of landing pages for locations which are very similar just with postcodes and location names being the main difference.I know you have tried to write unique content and specific location information but it still feels very similar and over-optimised purely written as an aggressive way to rank in all these London locations. I would say your site could be classed as being full of doorway pages for all the locations and this is definitely something Google doesn't like and falls fowl of their guidelines thus hurting your ranking ability. You also don't appear to have physical locations in these places so they are more of a service area. As you aren't ranking at the moment I would personally cut everything back focus on ranking for your actual physical location then you may want to choose service areas and build some pages around these, but you don't want to overdo this and you definitely don't want a cookie cutter approach. Look to build pages that really are unique. You also need to look at building the main service areas you cover into your main navigation not at the bottom of your page.

Here is an article on Search Engine Land which addresses this very well and gives you lots of points to consider in order to help you get your site sorted and hopefully ranking - http://searchengineland.com/local-seo-landing-pages-2-0-222583

Have you also looked at how others have ranked for the main terms you mention above? Competition that is successful is always a good place to look

Hope this helps!

Matt