Entries to sit AS levels have fallen by almost 60 per cent on last year, provisional figures from Ofqual show.
The number of GCSE entries in 2018 increased by just under 1 per cent compared to 2017, but there was a fall across all non-English Baccalaureate subjects except art and design.
A level entries dropped slightly by 3 per cent on last year.
Entries for English A-level subjects have fallen by 14 per cent since 2016.
Overall entries for AS subjects in England fell from 659,880 to 269,090 in 2018, continuing a declining trend which was seen in 2016 and 2017.
In 2015, AS-level entries stood at 1,331,955, meaning that entries have now cumulatively dropped by 1,062,865.
Ofqual said that the drop is “largely due to the decoupling of AS from A levels”, which has meant less schools are interested in offering the qualification.
Elsewhere, the overall entries for GCSEs in England increased by under 1 per cent 5,098,030 in 2017 to 5,136,495, which Ofqual said was mostly due to a rise in entries to EBacc subjects.
However, all non-EBacc subjects saw a decline in entries except art and design subjects, which saw the number of entries increase by 2 per cent.
Modern foreign languages have remained relatively stable compared to the significant drops of previous years, with German entries up by around 3 per cent and Spanish up by 8 per cent. French was down by 1 per cent.
At A-level, entries decreased from 785,450 in 2017 to 759,670 in 2018. Most subjects saw a decrease, but there were notable increases in entry in computing (up by 25 per cent) the sciences and mathematics (up by 3 per cent).
Since 2016, of the subjects with relatively large entries, the biggest proportional decrease in entries has been in A level English subjects, which have fallen from 78,795 entries in 2016 to 67,685 in 2018 – a 14 per cent drop.
Headteacher unions criticised the decline in AS level and non-EBacc GCSE entries.
Geoff Barton, general secretary of the Association of School and College Leaders, said: "The government’s decision to ‘decouple’ AS levels, so that they don’t count towards A levels, has made these courses increasingly unsustainable in schools and colleges, and means students now tend to take three subjects instead of four in this phase of education.
“The evidence is clear that the government’s reforms have led to reduced subject choice for students and a decline in creative arts and technology entries."
Paul Whiteman, the general secretary of the NAHT heads' union, said: “It is now impossible to argue that the EBacc measure is not having a narrowing effect on young people’s choices at GCSE.
"These reforms put schools in an impossible situation where they must reduce the opportunities they offer to pupils in order to satisfy an arbitrary government target."