You can do the SRC (Short Range Course) in any RYA recognised centre. Have a look at www.rya.org.uk
for a list of courses.
It is usually done over one day or two evenings. You will then receive a licence after paying £19.
To legally use a radio you will also need a Ships Licence which is required for fixed VHF radios as well as hand held. This costs £15 a year. Have a look at www.radio.gov.uk
Basically you need BOTH before being able to legally use your radio.