You should always consult with an immigration attorney before applying for citizenship. In general, one is able to hold both U.S. and U.K. citizenship at the same time. See the following websites for more information:
You wont lose your UK citizenship.
Business Immigration Attorney. For H, L, J, EB5s, PERM and EB1/2/3 Petitions. Call 800-688-7892 or visit www.ImmigrationDesk.com. Law Office of Anu Gupta. The advice suggested here is for general information only and not to be construed as legal advice.
It's unlikely you will lose your UK citizenship in this scenario, but best to consult with an immigration lawyer who will understand your unique situation once you get a little closer to the time to make sure that's correct.
This is not legal advice and no attorney-client relationship has been formed, now or in the future. This is just a casual opinion expressed about a hypothetical situation.
U.S. law does not determine whether or not the U.K. will consider you a citizen. You may wish to consult your consulate about that question before you file.
The above is intended only as general information, and does not constitute legal advice. You must speak with an attorney to discuss your individual case.