Question : UK bank account number and sortcode checking algorithm needed

Hi experts,

I'm trying to create a direct debit web app but need a method of checking whether a bank account number and sort-code which have been entered into a web form are valid.  I know there is some sort of algorithm for checking the validity of these because there is an online tool  at http://www.iban-bic.com/iban_und_bic.0.html?&L=2 which validates account details given the country, account number and sortcode but I can't seem to find an algorithm that works.  I have tried the one used for credit cards where you double alternate digits, sum them then mod 10 the result but this doesn't seem to work!

Answer : UK bank account number and sortcode checking algorithm needed

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