Can I buy the Samsung official extended battery for the UK Galaxy Nexus?
Engadget has a great comparison shot of the battery differences between the HSPA+ and LTE versions in their review of the Verizon (LTE) Galaxy Nexus. The short answers seems to be 'no'; the link you provided is to an extended battery for the LTE Galaxy Nexus and therefore wouldn't be compatible with your HSPA+ version.