The unverified listing gives 01442 422005 as Customer Credit Services beside the 0845 number you quote. This is a Hemel Hempstead number.

a very nice man wrote on Aug 13^th, 2006 at 3:52pm:

I'm not sure how you've found that S1 2US goes to the Pond Hill/Street. Then I remembered that the main Royal Mail delivery office is situated on Pond Street, hence that area will probably be S1 1AA. This made me think that it might be a PO Box, but now I'm not so sure.  I have found this page that says it's PO Box 1321.

Multimap shows S1 2US to be the southern end of Pinstone Street, at the juncture with Furnival Gate. Branches in and around Sheffield are listed on HSBC's website here. All have fax numbers starting with 0114 2604/5 which suggests that HSBC has a block of numbers that it uses for branches within the 0114 area.

I Googled hsbc "0114 293" which comes up with a couple of hits.

One has the address:
HSBC Bank plc, Griffin House Pennine Centre, Sheffield, South Yorkshire, S1 3GG

192.com lists 0114 252 8000 as the number for that address.

the closest number i could find was 01792 306000 which goes through to the Swansea Customer Service Centre. Apparently Customer Credit Services work in the same building.