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

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. 

Hi Jim,
I agree with adg101. I believe the benefits of bi-wiring likely become greater when running speakers with large, power-hungry low frequency drivers. For your Wharfdales, I would simply run those HT Pro 11+ cables, or your GHs, full range to the MF/LF terminals, use some high quality jumpers to the HF and enjoy the music.
I would consider using jumpers made with something like this:
http://www.partsconnexion.com/wire_hookup_neotech_cu_tef_sc.html
Since these are solid core wires, you can easily use a single wire without connectors as jumpers.
If you jump from the MF/LF posts to the HF posts, I would probably select the 16-18awg wire. If you jump from the HF posts to the MF/LF posts, then I would use the largest 12awg wire. Four 6-10 inch pieces should work just fine. They also offer the same OCC wire as stranded, which may be kinder to your HFs. You may need spades or banannas if you use the stranded wire.
http://www.partsconnexion.com/wire_hookup_neotech_cu_tef_st.html

Somewhat on topic. I just went to a bi-amp setup with my VR 33's and read in a review that the internal cabling of the speaker was Analysis Plus 14 gauge. Since I need new wire to replace my current bi wire cable (Morrow sp-5), I was wondering about cable matching to the internal wiring. Looking at the costs for some of the Analysis Plus cabling being sold here on Audiogon would there any benefit of much more expensive cabling outside connecting the speaker than there is internally? I could save hundreds but wouldn't realize what the actual difference would be without hearing both. Don't have much experience with system setups. Any feedback would be appreciated. Thanks.

As some have mentioned previously, talk to a dealer for ideas of cables that might sound good with your particular electronics and speakers.  I have owned various models of Vandersteen loudspeakers for the last 30 years.  His crossover networks are intended by design to be used with biwiring.  In conversations with the folks at Vandersteen they are quite emphatic that you not mix brands or cable topologies.  What I did to maximize quality and control the price of speaker cables to some extent was to buy two sets of Audioquest cables from the same "family".  The mid-high cable had the highest quality conductors and the bass cable was one step below in that family with slightly less pure conductors.  I am confident you could employ such a strategy with cables from numerous manufacturers.