In most cases, there is no entitlement to leave in lieu.
Full-time workers have a statutory entitlement to twenty days of annual leave and ten public holidays. Teachers on leave will generally have sufficient days of paid leave through scheduled school closures, outside their Maternity leave, to address this entitlement.
However, if you’re starting your maternity leave in spring, and you’re going to be on your leave through both the Easter and Summer closures, you may be entitled to take a small number of days of annual leave in lieu immediately before your maternity leave begins.
Please see the more comprehensive explanation here and Chapter 10 of circular 54/2019 (PDF) for further details.