There isn’t fixed criteria on shared ownership deposits. Different mortgage lenders will have different criteria on how much mortgage deposit they will require.
This will be based generally on your affordability and the value of the property.
As with other mortgages where a 0% mortgage deposit is available, you may be able to get one with a shared ownership mortgage based on the mortgage lender and the type of product they have available.
As with all mortgages, the higher the deposit the better the loan to value and in almost all cases, the better the rate you will receive on your mortgage.
Tip: Remember the mortgage on a shared ownership property is calculated based on the number of shares in the property you are trying to purchase and not the full value of the property.