Cheque Mate

I bank with Abbey, I always have. My parents set up an account for me when I was a small child. As I grew up I stayed loyal and kept my banking with them as I'd never encountered any problems.
Until now.
Last wednesday I put 2 cheques totalling £100 in an envelope and paid them in using the cheque payments box. It's now thursday, eight days later, and only one of the cheques has been paid in.
So where has the second cheque gone?
I'll be heading to Abbey for a fight this afternoon.