It's very important to find a center that matches the sonic signature of your left and right channel speakers. If they don't sound alike, a voice will change tone and 'weight' as it pans from left to center to right. It's not impossible to mix and match different brands to get good sound, but if your main speakers are 'forward' and the center you choose is 'laid back' (or vice versa) it's just not going to sound right.
From your post I assume that your main left/right speakers are 5+ years old. If you are happy with your current speakers, you might try to see if the manufacturer made a matching center and look for it on ebay/craigslist type sites.
If you must buy either the Wharfdale or Cambridge, see if you can take both home for a few nights to see which one sounds like your existing speakers. The easiest way to do this is to temporarily replace one of your main speakers with the center and play some music you are familiar with (in stereo).
If this is your first step in upgrading your entire system, buy the center that matches the rest of the speakers you like.
Both are reputable companies that make quality products, but only you can say which one sounds better to you. A buddy of mine loves his Klipsch speakers (horn tweeters), but they sound way too bright to me. He thinks my Polk LSi sound too laid back. Neither of us are right or wrong, we just have different tastes.
Good luck with whatever you decide!