When is cash interest "realised"?

Hi, I am looking to open a savings account that will give me interest on cash (not stocks/shares/bonds/etc). The interest is accrued and paid into the account monthly. It's likely that by the end of this tax year, I will go over my personal savings allowance as outlined in the "Tax on savings interest page" (https://www.gov.uk/apply-tax-free-interest-on-savings). I have been told that the tax paid is based on when earnings are realised rather than when gains are made, and the page also mentions how HMRC would automatically amend my tax code if I am employed. This leads me to a few questions: - When is cash interest "realised"? In my case, as it is paid into my account monthly, even if I do not make use of the money is it still considered realised every month? - I am currently in full-time employment and have my taxes taken through from PAYE. However, my employer would not be privy to any gains I make on cash interest. If HMRC amend my tax code, are there any actions I need to take from my end to notify my employer of a tax code change? Overall I just need a little clarity on cash interest gains and if there's any actions I need to take.

Hi,

If interest is paid monthly then when paid into your account will then be realised.
At the tax year end the banks and building societies will notify HMRC of the untaxed interest. Once received your record will be reviewed and if any tax underpaid a calculation will be issued to you.
The underpayment will be collected in the next tax years tax code.
If a new tax code is issued we will also send a copy to your employer. 

Thank you.