You will qualify for a student exemption or be disregarded as a student if you meet the Council Tax definition of ‘student’. Having a Tier 4 visa is not necessarily sufficient to meet this definition.
You will count as a student for Council Tax purposes if you are:
(i) under 20 years old, and studying for a qualification up to or equivalent to A level or Higher Scottish Certificate of Education on a course lasting 3 months or more involving a minimum of 12 hours a week daytime study;
(ii) a foreign language assistant working in a school or educational institution and registered with the British Council;
(iii) studying and enrolled at an institution in the UK, or in another country of the European Union, on a course which:
(a) lasts at least one academic year, or one calendar year if your educational institution does not have academic years; and
(b) requires you to undertake the course for at least 24 weeks a year; and
(c) involves at least 21 hours study, classes or work experience a week during term.
The following information applies to you if you meet paragraph
(iii), i.e. you are undertaking a ‘full time course of study’. This applies from the day that your course starts, so be aware that some local authorities may charge Council Tax for the period from your arrival in the UK to the day before your course starts. You will stop being regarded as a full time student if you give up your course, if your institution terminates your studies, or if your course ends. You may therefore be charged Council Tax for the period after you have finished one course and are waiting to start another, but you should not be charged during any vacation periods that fall between terms or semesters whilst your course is ongoing.
Providing you meet the requirements at paragraph (iii), you may be considered to be a full time student for council tax purposes if you are:
- a distance learning student,
- writing up your thesis or dissertation (so long as you remain enrolled at your college or university during this time),
- studying full-time at an educational institution in Europe for part of your UK course, or
- studying full-time at an educational institution in Europe and are in the UK
- undertaking a work placement as part of your course.
You may not be deemed to be a full time student for council tax purposes if you are:
- living in England and Wales and undertaking a course with a work placement where the period of time on work placements exceeds the total combined periods of study or tuition, unless you are undertaking a course of initial teacher training;
- undertaking a condensed course, where the total period of study has been reduced to less than an academic or calendar year;
- undertaking re-sits or repeating part of a course that does not require 21 hours or more study per week;
- writing up your thesis or dissertation, and your college or university does not enrol students during this period;
- an NUS or Student Union sabbatical officer and are not studying full time (if you have not completed your studies then the situation is less clear);
being sponsored by your institution under the doctorate extension scheme and have completed your doctorate; or
- a postgraduate doctor or dentist.
If you are unclear about whether you covered by the definition of student for council tax purposes, or for what period you are covered, you should seek specialist advice.
Copied verbatim from UKCISA. And it seems to be quite comprehensive too.