Duplicated bank account numbers

87AFig

Are bank account numbers ever duplicated within a bank?
I took an advance on my mortgage, when i entered my sort code i put the last 2 digits incorrect. On investigation i found out that the sort code i entered does belong to HSBC (the same as my bank). Is it likely that HSBC would issue the same account number twice? 
Nationwide that sent my advance are investigation but i am super concerned that a large sum of money has landed in someone elses bank account. 

Brie

all bank account numbers for any sort code should be unique.  you may very well get the same bank account number for different sort codes.  

so - no you won't get 2 accounts both with 20-01-01 12345678

but yes you could well get 20-01-01 12345678 & 16-10-10 12345678