Cheers for that chrys... although Ive still no idea who petnet are... other than their website is down again.
What I cant see from your screen cap is the google 'ad choices' string that should appear just to the right of "rate your ISP".
As I cant see anything there Im assuming that its here where the ad has failed to load and what is causing the lag.
Im not sure why petchoices would be advertising, unless its something to do with 'google logic' ie kitz/kittens/pets..
What I have done is log into google adsense and put a block on both
www.petnet.co.uk & petnet.co.uk, which should hopefully ensure that no adverts should be served from them again.