Top Gear producer Andy Wilman has admitted the popular BBC2 show is in danger of running out of road.

Wilman, who is credited with turning the show into a global powerhouse since relaunching it with presenter Jeremy Clarkson seven years ago, warned "this incarnation of Top Gear is nearer the end than the beginning".

In a blog addressing criticism about the latest series, shown at 9pm on Sundays on BBC2, Wilman said he was looking forward to the end of the current run.

"Personally I'll be glad to see the back of it," he wrote. "We've done some good stuff this series, but we were too rushed and too knackered to get everything right."

Top Gear's ratings have been down this series – although at more than 5 million they are very high for BBC2 – partly because the show was moved to the highly competitive 9pm slot to avoid clashing with ITV1's The X Factor.

However, viewers have complained about the editorial direction it has taken – in Wilman's words, that "we've lost the plot, we've disappeared up our arses, we're scripting everything, we're predictable etc etc".

Wilman said the presenters – Clarkson, Richard Hammond and James May – were starting to become caricatures of themselves.

"I do believe we've now got the presenters playing to their TV cartoon characters a bit too much – Jezza the walking nuclear bomb, Richard the daft Norman Wisdom, and James the bumbling professor," he wrote.

He missed "the three mates who mooch along", pointing to a recent film about Lancias as an example where they recaptured some of the old spirit.

"I know James definitely feels that way, and Jeremy and I were saying the other morning how the Lancia film was a bit of a wake-up reminder that we can actually make good films just enthusing about cars."

He defended the show against complaints that it was becoming too scripted, instead arguing that "you're watching a show that's lost its innocence".

He said the show's success after relaunching in 2002 had not been expected, resulting in "surprise and delight on the presenters' faces".

"That innocence has gone now, as always happens, because that's the nature of TV," he said.

"You all know the main pillars of our editorial, and we do our best to entertain, but none of us are going back to that first flush of discovery. But although that's sad, this is not time for glumness because there's still so much to do."

He admitted that the show could not go on indefinitely.

"It's fair to say this incarnation of Top Gear is nearer the end than the beginning, and our job is to land this plane with its dignity still intact," he said.

"But ironically, that does mean trying new things to the last, even if they screw up, because, well, it means you never stopped trying."