The Radio Communications Act 1992 cover's you for using a marine radio in the case of an emergency:
Section 49 Emergency operation etc. of radiocommunications devices
(1) A person does not contravene section 46 or 47 by operating a
radiocommunications device, or having a radiocommunications
device in his or her possession, in the reasonable belief that the
operation or possession was necessary for the purpose of:
(a) securing the safety of a vessel, aircraft or space object that
was in danger; or
( dealing with an emergency involving a serious threat to the
environment; or
© dealing with an emergency involving risk of death of, or
injury to, persons; or
(d) dealing with an emergency involving risk of substantial loss
of, or substantial damage to, property.
(2) In proceedings for an offence against section 46 or 47, the burden
of proving any of the matters referred to in subsection (1) lies on
the defendant.
(3) Nothing in this section limits the scope of the expression
“reasonable excuse” in section 46 or 47.