DNS resolve problems? Or something else?

Hi there,

A word of warning: I'm not networking wizard, but that's why I'm asking this question :}

We have a BT Infinity in our home, and a few MacBook Pros, a PC, and some iPads using the network.

We've had our router replaced by BT several times as they've gone through upgrades and we've had slow network issues.

In Chrome (though similar issues happen in Safari), the problem I'm having is that some (not all) websites aren't resolving properly, especially google.co.uk. Very often if I manually type in google.com, the website comes up and works fine. Most of the time, google.co.uk won't. Right now I've just typed in debenhams.com and I get the message "The DNS lookup failed". It happens to various websites, but obviously Google is most annoying - maps, images, shopping, any of the Google pages struggle to come up at least 50% of the time. Strangely, Gmail seems to work fine.

I've tried to flush my DNS cache using "dscacheutil -flushcache" in Terminal. I'm not sure it did anything because it just gave me a new prompt, but we have a 2nd MacBook Pro in the house having the same problems.

I've changed the channel on the router back and forth numerous times, cleared the browser's cache, reset the browser, tried other browsers, reset the router, etc. None of those have made any difference.

Under System Preferences > Advanced, what should the DNS server be? It's automatically set to one address, which is the same as my router number - is this correct?

The error message that sometimes comes up when pages won't resolve tells me my DNS settings may be wrong. If they are, how do I find out, and what do I change them to?

I should also note that sometimes I get an error message when the website won't resolve; other times, if it's google.co.uk and I've just typed something in the search field, the page just sits blank, no spinning wheel thing to show me it's thinking. It just sits there when I press the search or hit enter.

Sorry for being totally clueless... hoping someone can help!