The Roman Catholic Church in Spain has started a new offensive in a battle over plans by the ruling Socialists to liberalise the country’s strict abortion law.

The Spanish Bishops’ Conference (CEE) urged all Catholic MPs in the Lower House to vote against a Bill to allow abortion on demand. Bishop Juan Antonio Martínez Camino said: “Strict church doctrine says no true Catholic believer can agree with or support this move.”

Bishop Camino said those who participated in abortion would be immediately excommunicated.

Under the proposed reforms, abortion would be available on demand up to the 14th week of gestation. The new legislation would also offer abortion up to 22 weeks if a doctor certified a threat to the mother’s health or a risk of foetal malformation.

Beyond 22 weeks, it would be allowed only when doctors detected foetal malformation that they deemed incompatible with life.

The present law, passed in 1985, allows abortion within 12 weeks of gestation only in cases of rape and within 22 weeks in cases of foetal malformation. It allows abortion at any stage if a doctor certifies that a woman’s physical or mental health would be at risk if the pregnancy proceeded.

The most controversial part of the proposed reforms would give girls aged 16 the right to abort without consulting their parents.

Spain’s parliament, the Cortes, is expected to resume debating the Bill next month but the reforms may not become law until October.

Last week the Government survived an attempt by the conservative opposition Popular Party, which opposes the reforms, to halt the process.

Despite the Government’s determination to bring its abortion law in line with that of countries such as Britain, it faces widespread opposition. Three opinion polls found recently that most Spaniards opposed liberalising the law.

A total of 64 per cent of those surveyed in a poll for the daily El País opposed the measure. A poll for the conservative daily ABC found that 57 per cent of Spaniards “totally” or “relatively” opposed the measure. A third survey, published in La Vanguardia newspaper, put opposition at 71 per cent.

The Church and anti-abortion groups have waged an emotive media campaign. A video featuring aborted foetuses was shown to 15-year-old pupils at a Catholic school in Logrono, northern Spain. Pupils at Purisima Concepción y Santa Maria Micaela were shown remains of foetuses, alongside images of a laughing José Luis Rodriguez Zapatero, the Prime Minister.

Abortion is the most highly charged in a series of battles between Church and Government over reforms introduced since Mr Zapatero came to power in 2004, among them the legalisation of gay marriage, changes to divorce law and stem-cell research.