If I pay a bill by cheque or cash at the same bank as the biller’s bank, why doesn't my payment clear on the same day?

As a result of the implementation of a piece of European legislation called the Payment Services Directive, which came into force on 1st November 2009, if you pay your bill with cash at the biller’s bank, the cash will be credited to the biller’s account on the next business day.  However, the biller then has to take the data about all the bills paid into its bank account for that day and feed the information into its own systems so that it can apply the amount of the bill payments against each of its own customers’ accounts.  The time this takes is down to the individual biller companies.