However, when I connected my laptop to the test environment response times where much worse. It wasn’t the test environment as fiddler showed that back end performance was fine. My laptop was a higher spec than the client PC so I started up perfmon and observed high CPU as the main cause. However, it was not the Internet explorer process that was consuming the CPU but the McAfee intrusion protection process. Little known to me this was a recent corporate wide download (ok, I probably got the email about it but hey, I get a lot of emails!)
Moral of the story check to see if script scanning is enabled on yours abs the clients PC.