It is unusual to find UK pricing on software lower than in the USA so carefully check the credentials of the site offering the software.
May be worthwhile in contacting Adobe directly and asking but I suspect that you will be limited by the EULA
AFAIK you will need to provide to the supplier the name of your school and indicate whether you are a student, educator, or administrator. This may actually limit the install or upgrades depending on country of purchase - I do not know for sure
(c) Education Version. If we designate the Software or Service as for use by educational users (“Educational Version”), then you may only use the Educational Version if you meet the eligibility requirements stated at
http://www.adobe.com/go/edu_purchasing.
You may install and use Educational Version only in the country where you are qualified as an educational user. If you reside in the European Economic Area, then the word “country” in the sentence preceding this one means the European Economic Area.
This section of the EULA only states that you may install software in the country you are qualified as an educational user but no mention that the software must also be purchased in that country.