According to my local Asian supermarket guy, White Tower is a GREEK make, doesn't matter where it comes from of course provided it gives the BIR flavour. He does not stock it but he does carry 'KYKNOS' tomarto puree. I buy this in big tins and freeze it all in ice cube trays, 'pop' them out and store in a bag in the freezer.
It tastes a little different to the supermarket 'double concentrate' stuff, but not a great deal different.
Brill for bhunas and CTMs!