COVID-19 and other economic factors were having a dramatic effect on many companies in Britain, creating a "once in a generation" need for new equity, the company said.
Many companies have been kept afloat by state-backed loans since a lockdown in March tipped the economy into recession and there may not be full recovery until 2022.
Schroders said the money raised will be split between private and public investments.
Neil England, chair of Schroder British Opportunities Trust, said the pandemic has created investment opportunities in many established, high growth businesses that are currently "mispriced".
"Several of these companies have already been identified as candidates for early investment," England said.
The offer opens on Tuesday, with shares due to start trading on the London Stock Exchange on Dec. 1.
(Reporting by Huw Jones, editing by Sinead Cruise)