Ensuring the first diploma results are reliable and delivered on time will present “challenges”, the exams regulator warned today, as it admitted the timetable for checks had already slipped.

The news comes in reports published by Ofqual that reveal the extent to which overseas labour is now used in the GCSE and A-level marking process, with exam boards using centres in the Philippines, China, India and Australia.

This summer should see the first pupils complete the Government’s new diplomas receive their results. But the complex nature of the controversial new qualifications means compiling the results presents a host of potential difficulties.

Diplomas are made up of six compulsory components, four of them formally assessed qualifications which can be taken separately with at least 25 exam boards. Marks are then brought together for the complete diplomas, which are awarded by four boards.

Ofqual says there are “potential risks” with the two computer systems needed for the process - one to register students with a “unique learner number” and a second to calculate the final marks.

The regulator was supposed to check this “aggregation” of marks in a trial earlier this month. But it revealed today that the test has been deferred until July because “the necessary data is not yet available”.

However, Ofqual is content that the arrangements in place will allow diploma results to be delivered this summer.

Any glitches would cause alarm as the process will become increasingly complex as more of the diplomas are phased in.

This summer will involve only the “several hundred” students who chose to complete one of the first five diplomas - construction; creative and media; engineering; IT and society; and health and development - in a single year.

Ofqual says it is satisfied with exam boards’ quality assurance procedures for their overseas operations involved in British GCSE and A-level marking.

Edexcel expects 12.5 million answers from 133 different papers to be marked in a centre it has used in Australia since 2007. But they will be “clerical items” that do not require specialist knowledge to mark.

AQA uses agencies in India, China and the Philippines to key in single-word or multiple-choice answers from candidates that are then returned to the UK for marking.

This summer, exam boards in England, Wales and Northern Ireland will process nearly 8 million GCSE and A-level entries from students, mark more than 21 million exam papers, employ and train some 50,000 examiners and deal with some 150,000 queries from schools and candidates.

Ofqual said it was “confident that awarding bodies will complete the marking within deadlines and ensure that marking is appropriately quality assured before the publication of results in August”.