Presuming you have all ready paid tax on the money in the UK, there is no income tax ramifications on a transfer.
I hope that on that sum, you have been filing all of the necessary FBAR and FINCEN reports. Here are a couple of links you should read and make sure that you are in compliance with the reporting.
https://www.irs.gov/businesses/small-businesses-self-employed/report-of-foreign-bank-and-financial-a...
https://www.fincen.gov/report-foreign-bank-and-financial-accounts
