Slow innitial connection?

I've got a strange issue on my broadband connection at work.
When i try to open a webpage (ie bbc.co.uk, or microsoft.com) it takes about 20 seconds to open the webpage.
Once on the webpage, i can open any sub-pages on that particular site within a second, but trying any new sites, the same occurs - 20 seconds or so to open page then all sub-pages open almost instantly.
I'm stumped. Any suggestions?

It's a BTconnect account btw.

Can you drop me a PM(private message) with your phone number the service is installed on, your btconnect logon I think it will be A05564531 etc also your geographical location. Along with your Name, a number to contact you and the best time to call.

This is very similar to issues being experienced by residential customers.