Is it necessary to use the same cable brand and model for bi-wiring??

All of audio is about tone control. What difference does it make if I change speaker around to suit my cables, or change cables around to suit my speakers?
People basically change gear/cables around to suit their personal tastes. It's nothing to make a fuss about.

Put 10 audiophiles in a room to discuss biwire, and they will emerge with at least 11 different theories.

The majority of speakers today have biwire connections, however only a minority have been specifically designed for this from the ground up. For the rest it's just an add-on to maintain audio fashion. The manufacturers of the speakers that are specifically designed for biwire only recommend using two separate runs of identical cable for the biwire. So it appears they think it is necessary.

I agree that changing cables can make a difference in tonal character of the sound, however IMHO it doesn't make common sense to try and change high and low inputs on a speaker separately. That could cause an imbalance of frequencies at the crossover point.

Thanks to all who have contributed to this thread.  Let me assure those who responded, I am not using cables as tone controls. I just want to see if there is a qualitative improvement in sound, and to find this out with moderate expense.   The single cables I currently use are the Grover Huffman "EZ"  ( not sure what that logo stands for. o bought the cables from a sound engineer who works for Warner Brothers. He raved about their sound, ands was pretty much on the mark. I also have a pair of Harmonic Technology Pro 11+ which were highly touted and rightfully so. The only probably they are thick fire hose girth and a 12 ft pair.  That is why I was asking about speaker cables for bi-wiring the Wharfdale  Denton monitors. which are excellent.  

Well it sounds like you have two dissimilar pairs of speaker cables already. So you can try the experiment on your own. I've done it, don't worry, you won't blow anything up.
See for yourself if it works or not, let your own ears decide.
Let us know what you think.

Oh, and I have used cables as tone controls. I think everybody does, some just don't like to admit it. If you choose a cable that sounds best to you, in your system, then you are choosing the cable that matches the tonal qualities that you like best. Hence, using cables as a tone control.

I wouldn't get too hung up on spending a ton of money on speaker cables for your Wharfedale's which I'm sure is a nice set of speakers. A very good and neutral biwire jumper by Clear Day Cables will work just fine. All cables are some sort of a tone control, even ultra expensive cables. I'm using WyWires Silvers with Clear Day Jumpers and they work just fine; I have a set of WyWires jumpers coming so using my Clear Days for now. I've not heard your Wharfedale's but I suspect my Aerial's dig a bit deeper and I don't feel not running two separate runs of speaker cables is going to change things much; they sound pretty darn good as is. The point is people with much larger speakers that have more top and bottom end get along just fine with a single run with jumpers. I'd recommend buying the best single run you can afford and use quality jumpers over two pairs for the same amount of money.