Any interest earned as a result of the invested loans (other than as a result of the IFISA), is regarded as income and could potentially be subjected to income tax.
However, under the recent Personal Savings Allowance (PSA) regulations, you can earn between £500 and £1000 tax-free per year. This is dependent on your tax status.
You are responsible for accounting to HMRC and DWP any tax that is due and including details of your earnings as part of your self-assessment tax return. The rate of tax will depend on your overall income. Please refer to the following link:
https://www.gov.uk/income-tax-rates/current-rates-and-allowances for the current income tax rates and https://www.gov.uk/apply-tax-free-interest-on-savings for current UK savings allowances.
Please speak to a tax adviser if you require information about the effect of taxation on your personal circumstances.
Tax treatment depends on the individual circumstances of each client and the basis of taxation under tax legislation is subject to change in the future.