The freedom of Christians to wear crosses at work and to refuse to support same-sex relationships will come under international legal scrutiny at the European court of human rights.

Four landmark test cases in employment law will be argued before judges in Strasbourg on Tuesday, in hearings that may define the limits of religious liberty in the UK.

All four cases, already examined extensively in the English courts, involve practising Christians who allege they were discriminated against in the workplace.

Nadia Eweida, 61, a British Airways employee and Pentecostal Christian from Twickenham, west London, and Shirley Chaplin, 56, a geriatrics nurse from Exeter, complain their employers prevented them from wearing crosses visibly at work.

Lillian Ladele, a registrar of births, deaths and marriages from London, and Gary McFarlane, a Relate counsellor from Bristol, claim their dismissals constituted religious discrimination. Ladele, 52, declined to officiate at same-sex civil partnership ceremonies; McFarlane, 51, was accused of not providing counselling to same-sex couples. Both, according to the ECHR, believe “homosexual relationships are contrary to God’s law”.