Bridget Rosewell, chair of the independent review into planning appeals, which aimed to halve the average length of inquiries, was speaking at Planning's National Planning Summit this afternoon.
Among the 22 recommendations in the review report, published in February, was that the Planning Inspectorate (PINS) should adopt a 24-week end-to-end timescale target for appeal inquiry decisions.
Rosewell said was "no single cause" for why inquiries were taking too long, adding: "This is a process that just isn't working well right across the piste."
She said the recommendations focused on three areas - improving IT processes, earlier engagement by the appeal parties, and tighter scheduling of inquiries.
Rosewell said: "Many of the things we've recommended here are actually about making sure that the system is doing what it's supposed to do and making sure deadlines are hit.
"We are asking inspectors to be fiercer - to actually make sure that what's supposed to be happening is happening."
She added that the review wanted to see PINS be "more proactive" and "more robust", with inspectors needing to "actively manage and drive the inquiry process".
Rosewell went on to say that, in an effort to avoid legal challenges to decisions, a system had evolved where "the desire to achieve no challenge to your decisions has meant that inspectors have bent over backwards to accommodate slippage of time and changes to proposals, and that has dragged it out".
She added: "We've got to encourage inspectors to be more challenging.
"If that means you get some more court challenges and judical reviews, I think that's a worthwhile process to go through because it will be better on the whole and for all appeals, even if means that a few get challenged."
In response to the review, PINS yesterday published an action plan, setting out how it will deliver the recommendations.
Rosewell said she would jointly produce a report with PINS in September that would examine how the body is responding to her recommendations.
Full implementation of the recommendations was earmarker for June 2020, she added.