https://www.imperial.ac.uk/finance/financial-services/payroll/potential-hmrc-tax-code-fraud/
Potential HMRC tax code fraud | Administration and support services | Imperial College London
You can access or set up your personal tax account via the gov.uk website.
hmrc tax codeadministration and support
https://www.gov.uk/hmrc-internal-manuals/banking-manual/bkm509400
BKM509400 - Interaction of the Code with other measures: enablers of tax avoidance - HMRC internal...