Hi Dave!
Financial law and regulation mandates that we must store your data for 5-6 years after closing your account.
For PII (personally identifiable information), this is 5 years.
The legislation that underpins this is the EU 4th Anti-Money Laundering Directive enacted on 25th June 2015, which member states (of which the UK is still one) had to be compliant with by 26th June 2017 (http://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=OJ:JOL_2015_141_R_0003&from=ES)
The UK implementation of this was the The Money Laundering, Terrorist Financing and Transfer of Funds (Information on the Payer) Regulations 2017 (The Money Laundering, Terrorist Financing and Transfer of Funds (Information on the Payer) Regulations 2017). This updates & expands the The Money Laundering Regulations 2007 (The Money Laundering Regulations 2007)
For all other information relating to you it’s 6 years to reflect the Limitation Act (https://www.legislation.gov.uk/ukpga/1980/58) (i.e. how long you could bring a claim against us for breach of contract) or raise a Financial Ombudsman Service complaint.(DISP INTRO - FCA Handbook).
Hope that helps!