The Wellcome Trust has scrapped plans to move all staff to a four day working week, admitting it would be “too operationally complex to implement”.

The biomedical research foundation had been considering trialling the dramatic shift in working patterns this autumn, giving all 800 of its London-based head office employees Fridays off without a reduction in pay.

Had it adopted the policy, Wellcome, which is the world's second-biggest research donor after the Bill and Melinda Gates Foundation, would have become the largest organisation in the world to do so.

But a three-month study found that the work of those employed in back office and support functions, such as IT, finance and human resources, would have been made much harder by the move.

Other areas of the business more conducive to flexibility might have benefited by such a change but it was felt it was unfair to proceed, the Guardian reported.

There was also concern that compressing a full-time job into a four-day week could negatively affect the wellbeing of some workers.

Ed Whiting, director of policy and chief of staff, said: “After extensive internal consultation on whether we should trial the four-day week, we have concluded that it is too operationally complex to implement.