If the client you are developing channels for is blocking non-USA ip addresses, then you need to get them to make an exception for you. During the testing phase of your channel, you could set the channel properties to allow UK usage so that you could fully test your channel on a UK device.
Internally we use VPNs for international testing, so that is another approach, as long as you don't violate any agreements by streaming unauthorized content (i.e. Netflix and other content that is not available in UK).
- Joel