: Do you have any idea why they're going to the trouble to
: turn off the transmitter over the UK?

A balloon is an aircraft so that makes it illegal to transmit.
No transmitting equipment may be operated from an aircraft other than
type approved aviation band equipment under the control of the commander.

Some of the other replies are apparently forgetting we're talking about it
being illegal **while the balloon is flying over the UK**.

It is indeed legal **under U.S. regulations** to operate aeronautical
mobile. But U.S. regulations cease to apply once the balloon enters the
airspace of some other country. It would appear British regulations do
not allow for aeronautical mobile operation in unmanned aircraft.