An investor may elect under ITA07/S257AB(5) to have part or all of an issue of shares treated as though acquired in the tax year preceding that in which the shares were actually acquired. This is subject to the maximum annual investment limit for that earlier year (£100,000). The SEIS/ EIS rate for the earlier year is then applied to the shares treated as acquired in the earlier year and relief given accordingly.
For further information please visit the HMRC website.
Here are an example:
Wesley invests £20,000 in the tax year 2016-17 in SEIS qualifying shares. The SEIS relief available is £10,000 (£20,000 at 50 percent). Her tax liability for the year before SEIS relief is £15,000 which he can reduce to £5,000 (£15,000 less £10,000) as a result of his investment.