Wilman quit the long-running TV series in the wake of Jeremy Clarkson's departure and the BBC plans to relaunch Top Gear with new presenters.
But the TV executive, who alongside Clarkson, Hammond and James May, are believed to be negotiating with a streaming service like Netflix or Amazon, said of the show: "I don't think we'll see the like of it ever again."
Writing about the success of the show in the latest edition of Top Gear magazine, Wilman said: "The show that finally ground to a halt just over a month ago was a colossus.
"In our heads we were making a car show for car dweebs, but as series four went to five went to six, we realised that the actual growing was sprouting in directions we hadn't reckoned on.
"Because we never planned it, I don't think we'll see the like of it ever again."
He told how BBC management were unsure whether they wanted to keep Hammond after he made his first series in the Top Gear reboot.
"For a while, for some reason I cannot fathom, the BBC management had a wobble about Richard and in their usual, classic HR style said to him, 'We may not want you back for the second series, but, anyway, have a good Christmas'."
Things you never knew about Top Gear
Things you never knew about Top Gear
1/14 Top Gear isn't really for adults
It's 'aimed at people with a mental age of nine', according to executive producer Andy Wilman.
2/14 Planet Earth loves it...
Top Gear is screened in more than 100 countries worldwide and has millions of fans.
3/14 ...but not all motoring hacks do
You might think Jezza was a hero of the motoring hack world but that's not strictly accurate. Telegraph journalist Neil Lyndon summed Top Gear's 21st birthday last year up well: 'Does that mean Billy Bunter and his gang finally get forced out of the Fourth Remove and into long trousers?'
4/14 The Top Gear theme tune is a classic rock song
Seven-minute instrumental 'Jessica' by The Allman Brothers was a hit in 1973. Top Gear has recorded its own version now but used part of the original recording at first. One for the road trip playlist.
5/14 Jeremy Clarkson couldn't get much more controversial if he tried
The presenter is currently suspended from the BBC following a 'fracas' with a producer over a steak dinner. Past scandals include a string of racism allegations.
6/14 This Porsche caused all sorts of trouble in Argentina
The Top Gear team were forced to flee Argentina after locals took offence at the car's number plate - believing it was a deliberately provocative reference to the Falklands War of 1982.
7/14 If it's car-buying advice you want, look elsewhere
It's an in-joke in Top Gear that they don't do car tests. You would be mad to make a purchases based on Jezza's verdict.
8/14 Richard Hammond had a near-death experience filming Top Gear
The 'Hamster' was filming a Top Gear segment in a dragster called Vampire when its front-right tyre burst at 288mph. Hammond spent two weeks in a coma but luckily went on to make a full recovery. He requested that no mention of the crash was made in future Top Gear episodes.
9/14 Jeremy Clarkson is more than a little bit taller than Richard Hammond
Nine inches, to be precise.
10/14 Top Gear used to offer real advice
Before these lads took over, it was a real car-reviewing show with presenters such as Angela Rippon, who gave practical reviews of down-to-earth workhorses such as Cavaliers or Mini Metros.
11/14 Those 'reasonably priced' cars take quite a battering
Denis Chick, of Vauxhall, is brave to have lent the show a fleet of his Astras. He said: "Vauxhall Astra sales would not improve if everyone drove like Jimmy Carr around the Dunsfold track." The comedian hilariously took his test car's front off-side tyre clean off its rim.
12/14 Jeremy Clarkson is a YouTube star
Stray down the motoring internet hole and you'll find lovingly posted videos of 'Clarkson the early years' with incredibly loud hair reviewing 1990s cars in an oddly sensible manner. Very disturbing viewing.
13/14 There have been multiple Stigs
Racing driver Perry McCarthy was stuntsman The Stig on the first two series of Top Gear - here's the man under that famous helmet.
14/14 Ben Collins was The Stig for eight years
Ben Collins was The Stig on Top Gear for eight years. He left amid a clash with the BBC when he unmasked his identity and published an autobiography. Collins thinks Top Gear has 'lost some of its sparkle'.
Wilman complained that the show received many visits from the "BBC Meddling Department".
He said that on one occasion they "told us that market research showed our show was attracting young, lifestyle, trendy viewers to BBC2, so perhaps we should think about getting a young, lifestyle, trendy presenter".
"Ever keen to assist, we searched high and low and eventually came up with just the man: James May," he said. "At one point, the Meddling Department arrived bearing more news from the outside world. Nearly half of our audience, they now declared, was female.
"Before they had a chance to follow that up with the inevitable suggestion to get a woman presenter, we shooed them out and carried on."
The show constantly hit the headlines for controversies and Wilman said: "We made a Wall of Complaints as a home for the best and most vitriolic ones."
He said he would never forget Hammond's accident, in which he ended up in a coma when the tyre of a jet car blew at 288mph.
He added: "What I never had to worry about were the words coming out of the presenters' mouths. Any producer would be blessed to have those three. They would set off on a road trip, no script, just a few bullet points in their heads, and riff away like mates ... so much of their drivelly banter was gold."
His comments came as Clarkson is set for a return to the BBC, for an interview on the Radio 2 breakfast show with Chris Evans on Thursday morning.
The 55-year-old is expected to speak about his future in the studio tomorrow morning, in his first interview since being axed as Top Gear presenter following his attack on producer Oisin Tymon.
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