The accounting treatment needs to reflect the ‘economic reality’ of the scheme. These schemes can involve arrangements which can be complex. Here are some references which may help you get started.
Company share schemes – an employees guide
https://frazerjames.co.uk/company-share-schemes-an-employees-guide/
Issue of free shares to directors/employees
https://www.accountingweb.co.uk/any-answers/issue-of-free-shares-to-directorsemployees
IFRS 2, Share-based Payment
https://www.accaglobal.com/uk/en/student/exam-support-resources/dipifr-study-resources/technical-articles/ifrs2-pt1.html
Accounting for share awards
https://www.bdo.co.uk/en-gb/insights/tax/global-employer-services/accounting-for-share-awards#:~:text=Accounting%20processes%20for%20share%20awards&text=The%20’fair%20value’%20of%20share,or%20award%20has%20been%20made)
What’s the difference between issuing stocks directly to an employee and an ESOP?
https://www.cakeequity.com/blog/whats-the-difference-between-issuing-stocks-directly-to-an-employee-and-an-esop