Some of the UK’s top universities are failing to disclose the results of clinical trials, with experts warning that these unreported studies leave an incomplete and potentially misleading picture of the risks and benefits of treatments.

Previous research has found that around half of all trials go unreported, particularly those whose results are negative. And the World Health Organization (WHO) has warned that failing to report results can lead to the use of “suboptimal or even harmful products”.

Now, a report from pressure group Transparimed has found that UK universities have failed to publish the results of 1,671 clinical trials listed on both European and United States trial registries. And 19 out of the 27 UK universities studied have failed to upload a single missing trial over the past two months.

The report says that unless universities post the results of these trials soon, valuable medical research data will be lost forever. Failing to publish will also lead to duplication of research, much of which is publicly funded, the report warns.

Since 2014 there has been a European Union requirement for all clinical trials conducted by member states to be reported and registered, although there are no sanctions for institutions which fail to comply.