Vat Refund กับวีซ่าท่องเที่ยวประเทศอังกฤษ

The 12-month rule applies only to people who live in the UK-EU (students, residents)

http://www.hmrc.gov.uk/vat/sectors/consumers/overseas-visitors.htm

If you live outside the EU

If you are an overseas visitor, to qualify for a VAT refund you must:

live outside the EU
leave the UK for a destination outside the EU with the goods you have bought by the end of the third month after the month when you bought them
show customs officials the goods, your receipts for them and a completed VAT refund document when you leave the EU


You will have no problem whatsoever.