What is the difference between SEIS and EIS?

SEIS is aimed at start-up companies that have traded for two years or less. 

EIS is aimed at companies that have traded for seven years or less (although there is an extension to ten years for 'knowledge intensive' companies)

Under SEIS the investor receives a rebate of 50% of the amount invested, whereas under EIS this is at 30%.

Aside from the above differences, SEIS and EIS are almost identical. Companies will typically begin with SEIS and move onto EIS after two years.