Thanks for your reply.
Usually what would happen would be that you would inform them in writing that your relationship has broken down irretrievably with your wife and that you no longer consider that you have a relationship of man and wife. This would usually be followed by you stating that you intend to divorce and that as a result of this you no longer require her to receive a spouse visa.
The UKBA at this point would generally consider that the statement that your marriage is at an end is sufficient for them to take the marriage as no longer subsisting and therefor that she is ineligible for a spouses visa.
If you have done the above already then you should follow up your previous email by referring to it and asking for them to confirm that there have determined that she shall not receive a visa. The following day after you have sent the email you should give them a telephone call and check that they are taking the appropriate action.
If you have not done the above then you should write immediately. Obviously in the letter it is very important that you give full details of your wife, your and any application reference you have received so that they can easily trace the matter.
The UKBA/High Commission can be very, very slow in actioning things so that may be the case here. If she receives her visa and travels to the UK you can still inform the UKBA of the breakdown of the marriage. They would likely curtail her visa and ask her to return home.
If this is useful please kindly click accept so that I may be rewarded for my time. You will be free to ask follow up questions.