That phone number is a central phone number that covers all Barclays branches, but yes they could probably tell you the address. I think K13s answer is right- I googled it and got ( http://www.ummah.com/forum/archive/index.php/t -93353.html) which mentions Barclays Bank plc, Luton Group, PO Box 48, 28 George Street, Luton, LU1 2AD
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But I'd be interested to know what use the information is- can you tell us?