Only ten people filed a complaint but these were upheld and the adjudicators ordered that the ad must not appear again in its present form.
The Assessment states:
The ASA noted that the CAP Code stated that ads "should contain nothing that is likely to cause serious or widespread offence. Particular care should be taken to avoid causing offence on the grounds of race, religion, sex, sexual orientation or disability. Compliance with the Code will be judged on the context, medium, audience, product and prevailing standards of decency". We considered the use of a nun pregnant through immaculate conception was likely to be seen as a distortion and mockery of the beliefs of Roman Catholics. We concluded that to use such an image in a light hearted way to advertise ice cream was likely to cause serious offence to readers, particularly those who practised the Roman Catholic faith.
We noted that the number of complaints was relatively small but that the ad had been placed in a small number of publications only.
The article that prompted my complaint was brought to my attention by Amanda Lewin and was reported in the Mail Online.
The adjudication can be read in full at the ASA website.