UK Bank Account Modulus Validation

The existing bank account number validations for domestic banks only check the length of the bank account number. These validations are performed during the entry and update of bank accounts.With the account number validations for United Kingdom are enhanced to include a modulus check alongside the length checks.
Modulus checking is the process of validating bank account numbers in conjunction with the Banks Sort Code. A new concurrent program "Load UK Domestic Account Validations Data" has been provided to load modulus validation data files.

If you compare , you can understand this way :

Existing validations:
The sort code should have 6 numeric digits
The bank account number should have 6 numeric digits

New Validation:
The combination of Sort Code and Account Number should pass a modulus check.

Modulus check methods are prescribed by VocaLink (BACS technology partner) Modulus checking ensures sort code and account numbers are compatible before submitting BACS payment instructions.

In the United Kingdom (UK), Vocalink (BACS Technology partner) provides up to date details of the modulus checking methods in use for a number of UK banks and financials institutions to validate UK Bank Account and to sort code numbers, along with the required weighting tables and sort code substitution data. An algorithm can be used along with these tables to validate the bank account.

There are three types of modulus checks that are performed on the UK bank accounts.

Mod 10 - Standard 10 modulus check
Mod 11 - Standard 11 modulus check
DB1A1 - Double alternate modulus check

This feature enhances the existing UK bank account validation model by introducing modulus check validation. A modulus check will be performed during the creation and modification of the bank accounts and will also be applied on the importing of bank accounts through public API's.

When the bank accounts are entered, the system will now invoke a new modulus check, in addition to the existing length check (8 digits) for validating the UK bank accounts. The modulus algorithm applied on the bank accounts depend on the bank sort codes and is part of the sort codes published by Vocalink.

The solution introduces two new concurrent programs for the load and maintenance of the modulus weights table and Sorting and Substitution data file used in the validation process.

List of banks that support modulus checking
Allied Irish HSBC
Bank of England Lloyds TSB
Bank of Ireland NatWest
Bank of Scotland Nationwide Building Society
Barclays Northern
Halifax Woolwich
Orwell Union Ltd Citibank
Royal Bank of Scotland Clydesdale
Santander Co-Operative Bank
Secure Trust Coutts
Ulster Bank First Trust
Virgin Bank Yorkshire Bank