I have had the great misfortune of having to respond to freedom of information requests and privacy breaches for a very large public sector organization.
Not in the UK but very similar legislation.
Some issues are simple, many are not. Many FOI requests came from people who were dissatisfied with decisions affecting them. Sadly, many held beliefs that the agency was lying, was in cahoots even with Her Majesty the Queen. Etc etc.
It takes a lot of work to review and redact the required info, to index it, and then disclose. Hours and hours of work which takes away from other work. I can understand the need for extra time.
I remember one instance that took weeks of work, and resulted in two large boxes of documents being sent to the requestor, who then became even more demanding because he was sent too much.
In this case there will be endless documents, including emails and the like that will need to be reviewed and redacted.
I do think the extra time requested is excessive. It defeats the purpose of FOI provisions. But protecting the privacy of the participants in the trials is important.
Surely there is a medium ground.