The Newbury and District Amateur Radio Society(NADARS) are running an Intermediate courses in 2023. I did my Foundation course with NADARS and they run an excellent course.
The RSGB defines the syllabus for the three levels of Amateur Radio Licence. Each License requires a separate exam, which these days can be done on line. Training is probably best done face to face because it is easier to ask questions and interact with the lecturers. Licenses are issued by OFCOM once a pass is obtained.
The different level of license allow use of different transmission power and facilities.
Details of each of the syllabus can be found on the RSGB website.
Details of the NADARS courses can be found using this link https://nadars.org.uk/courses.asp
The next scheduled courses are:
Intermediate commences on the 18/19 March 2023