Really weird latency issue

I've got my home and mobile both on vodafone. I'm have a really weird problem connecting to some of my websites where they have a >12s delay in connecting with the website - each and every time.Some details

if I connect through my phone via 3g it's quick

if I connect through my phone via wifi it's slow

if I connect via a laptop on wifi it's slow

if I connect via my desktop computer on ethernet it's slow

websites running software A are affected

websites on the same server running wordpress are fast

A tracert on my sites give very similar results

A request for an image on the affected site will be fast

this is all points to a problem with the script however when others try to access the slow or fast sites they have no issues - or if I go through a proxy it is fast.I use google's dns settings but have changed them to Vodafone's and that made no difference.I'm all out of ideas on how to debug this. Can anyone point me in the right direction?