The reporting fund regime is a set of rules implemented by the UK government to regulate the taxation of offshore funds. These rules apply to funds that are based outside of the UK but have UK investors. 

Under the reporting fund regime, funds must report their income and gains to the UK tax authorities, and the investors in these funds must pay tax on their share of the profits. The regime ensures that UK investors in offshore funds pay the correct amount of tax on their investments. 

Excess reportable income (ERI) is the amount of income profits generated by a reporting fund that is in excess of the amount that is distributed to investors during the course of the accounting period. This excess income must be reported separately to HM Revenue and Customs (HMRC) by the fund manager and made available to investors who will be liable to tax on this income in addition to their regular tax liability.