You can only switch into Tier 2 if you meet the following criteria:
• you must have current leave which has not expired in one of the eligible categories
listed above; and
• you must have successfully completed and passed a UK recognised bachelor or postgraduate degree, Postgraduate Certificate in Education or Professional Graduate Diploma of Education or have completed a minimum of 12 months study in the UK towards a UK PhD during your current period of leave or a period of continuous leave1 which includes your last grant of leave; and
• you studied for the eligible award at a UK institution that is a UK recognised or listed body, or an education provider which holds a licence for sponsoring students under Tier 4 of the Points-Based System; and
• you are applying from inside the UK
个人理解这段话对你最重要的是during your current period of leave or a period of continuous leave which includes your last grant of leave红字部分，我的理解是你可以申请的，它说的是要么在当前持有的签证有效期阶段读完的课程（during your current period of leave，这个显然对你不适用 ），或者是在包括当前签证有效期在内的一段连续的时间内读完的学业（应该是你的情况），这段时间内你的签证必须要连续，并且持有有效的可以允许你读这个课程的签证，也就是学生签证。
If you are switching from Tier 4 or the former categories of student, student nurse, student re-sitting an examination, overseas qualified nurse, person writing up a thesis, postgraduate doctor or dentist or student union sabbatical officer, you must have current permission to stay in the UK and, during that permission to stay, you must have lawfully obtained a UK degree, postgraduate certificate in education or professional graduate diploma of education. This does not include, for example, vocational qualifications at degree level which are not degrees. If you are a PhD student, you do not need to have completed your course, but you must have completed at least 12 months’ study towards it in the UK.
You must have obtained one of the named qualifications above:
at a UK institution that is a UK recognised or listed body, or one which holds a sponsor licence under Tier 4 of the points-based system; and
during your most recent period of permission to stay, or period of continuous permission to stay that includes your most recent permission to stay - this must have included permission for you to study for the qualification.
(d) An applicant under the provisions in (b)(ii) above must meet the following requirements:
(i) The applicant must have completed and passed:
(1) a UK recognised bachelor or postgraduate degree (not a qualification of equivalent level which is not a degree),
(2) a UK Postgraduate Certificate in Education or Professional Graduate Diploma of Education (not a qualification of equivalent level),
or the applicant must have completed a minimum of 12 months study in the UK towards a UK PhD.
(ii) The applicant must have studied for the course in (d)(i) at a UK institution that is a UK recognised or listed body, or which holds a sponsor licence under Tier 4 of the Points Based System.
(iii) The applicant must have studied the course referred to in (d)(i) during:
(1) his last grant of leave, or
(2) a period of continuous leave which includes his last grant of leave.
个人理解是最多追朔到last grant of leave, 如果是psw的话, 那么那个学位课程就不是在规定的特定时间段内进行的.
我个人的理解是这个也是可以的，只要你所有的签证都是连在一起没有断开过，因为during your most recent period of permission to stay, or period of continuous permission to stay that includes your most recent permission to stay - this must have included permission for you to study for the qualification里面对你最重要的是红色部分。首先是要continuous，也就是说你曾经持有的学生签证和psw签证要和现在的签证之间不能有gap。其次，这段连续的签证没有断开的期间，必须包括你用于获得学位的那个学生签证，所以你只要符合这个要求应该是可以的。
还有另一种情况，比如你08年9月-11年1月学生签证并获得了本科学位，但是11年2月才申请了2年psw，后来12年9月又申请了学生签证读现在的学位。这样尽管psw和现在的签证是连续的，但由于你psw和前面的学生签证断开了，当中有1个月gap，这3个签证就不能算一个连续的签证期间，那么一开始获得本科学位的学生签证就不能和当前签证算在一个period of continuous permission to stay。这种情况下就不能转tier 2.
