You are able to claim income tax relief upon receiving your S-EIS3 certificate from the business. The timings for the company issuing this document can be found here -
https://www.spondoo.co.uk/tips/i-have-invested-in-an-eis-or-seis-business-when-and-how-do-i-get-my-tax-relief/.
However, if you do not hold the shares for the required 3 years, the following tax issues will become relevant:
For expert advice on EIS and SEIS please reach out to us.