Forty per cent of community schools (state schools controlled by the local council and not influenced by business or religious groups) are also not teaching enough RE at Key Stage 4, according to the National Association of Teachers of Religious Education (NATRE).
State schools must teach RE to all pupils, whether they are studying for a GCSE or not.
However, NATRE says schools have hid behind failing accountability structures, with 64 per cent of students in year 11 and 59 per cent in year 10 not being taught RE.
More than a third of schools reported that they have received no subject specific training in the last academic year, with Ofsted saying school leaders, including governing boards, will be held to account when a lack of training for teachers has a negative impact on pupils.
NATRE's research found that almost 40 per cent (up from 34 per cent in 2015-16) of community and 50 per cent of Academy schools without a religious character do not meet their legal or contractual requirements for RE at Key Stage 4.
In 58 per cent of schools the number of specialist teachers of RE either remained stable or increased but more than a quarter of schools reported that the number of specialists in their school had fallen.
Three quarters of respondents reported that some of the subject was taught by teachers who primarily taught other subjects and in 36 per cent of cases more than 1 in 5 lessons is taught by these teachers who usually teach another subject.
Commenting on the research, Ben Wood, NATRE Chair, told Premier how schools are managing to disobey the law: "They're getting away with it because nobody is calling them out on it, thats the blunt eality of it. Ofsted sometimes do but they have a lot of things to look and obviously Ofsted aren't in every school all the time."
"Some schools say they're doing RE but what they're doing is combining it with it with Life Skills, PSHE, citizenship and maybe using a couple of days a year. So, they're not providing a high quality RE curriculum but the problem is because they say they're doing it, that comes across as if they are doing it."
NATRE is urging the government to establish a National Plan for RE as recommended by the Commission on Religious Education.
A Department for Education spokesperson told Premier: "Religious Education develops children's knowledge of the values and traditions of different faiths and cultures. It also fosters understanding between different faiths and cultures. That is why Religious Education is compulsory at all four key stages.
"The proportion of time secondary schools spend teaching RE has remained broadly stable over recent years while religious studies remains a popular GCSE.
"If there are concerns that a school is not teaching RE throughout then, in the first instance, these concerns should be raised with the school or Trust. If concerns are not resolved via this method they can be referred for further investigation."
More than 80 per cent of schools do not plan to make any GCSE RS Short Course entries in 2018/19, which represents a rapid decline (50per cent) since 2012 and 16 per cent reported no entries for the Full Course.
Parents do have the right to withdraw their children from religious education and do not have to give a reason for this.
At a national level the percentage of all teaching hours in secondary school spent on teaching RE was 3.2 per cent in 2010 and 3.3 per cent in 2018.
If a parent is concerned about the amount of RE being taught they can contacts their school's trust, the local SACRE (Standing Advisory Council for Religious Education) in the case of maintained schools or via the Department of Education in the case of academies.
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