1. It rules the internet

Forget the Reith Lectures or David Attenborough's latest wildlife epic. The most popular show on BBC iPlayer last year was the Top Gear team's geographically illiterate search for the source of the river Nile, with a staggering 3.4m requests.

2. It's not known for its liberal views

Download the new Independent Premium app Sharing the full story, not just the headlines

Oh, they are cheeky chaps on Top Gear. Last month one of them posted a funny picture on Twitter of Jezza (that's Jeremy Clarkson) asleep with a sign in front that read, "gay ****". Ben Summerskill, chief executive of Stonewall, is, like many of us, fed up with it all. He said: "Now they're 21, perhaps the boys will grow up?"

3. It's not really for grown-ups, anyway

In Radio Times last week, the show's executive producer admitted the show is "aimed at people with a mental age of nine".

4. It's not universally loved by motoring hacks

You might think Jezza was a hero of the motoring hack world, but that's not strictly accurate. Neil Lyndon, the Sunday Telegraph's motoring correspondent, sums its 21st birthday well: "Does that mean Billy Bunter and his gang finally get forced out of the Fourth Remove and into long trousers?"

The mysterious Stig

5. Don't expect car-buying advice

It's an in-joke in the show that they don't do car tests. You would be mad to make a purchases based on Jezza's verdict.

6. 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.

7. It used to offer real advice

Before the lads took over, it was 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.

8. The world loves it …

Top Gear is already screened in more than 100 countries.

9. ... but not Mexico

A run of borderline-racist slurs about Mexico when testing the country's first sports car didn't go down well several seasons ago.

10. The "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.

Jeremy Clarkson leans against a sadly dated car

11. It makes the BBC a fortune

The three middle-aged men have brought the show to the front of the BBC's commercial arms global profit drive. Last year shows such as Doctor Who and Top Gear made the BBC's commercial arm more than £300m.

12. And Clarkson doesn't do badly

Last year Jezza netted more than £14m from the show, the real engine of his wealth being the BBC buying out his 30 per cent shares in the company he set up to exploit the show's commercial opportunities. That's enough for 140,000 speeding tickets.

13. It's not for girls

When the show relaunched in 2002, the BBC wanted to hire an unnamed female presenter. Her agent also sent along Richard Hammond, then a former local radio presenter working on an unheard-of cable channel. Sadly for the automotive sisterhood, it preferred him.

14. Even Jezza is bored by cars

In 2002, Jeremy was only available because his BBC chat show had flopped. Prior to that he was bored with cars, and after testing one car couldn't think of anything to say about it.

15. There's a waiting list

Watching the lads' banter is so popular there is a lottery-type draw for audience tickets to each series.

Jeremy Clarkson, pictured here in 1995

16. World domination

The show will front a new global BBC Brit channel which the corporation hopes will fill a "gap in the global market". Apologies, world.

17. Women watch it

Oddly it seems up to 40 per cent of Top Gear viewers are women.

18. Complaints, it's had a few

The BBC has responded to complaints on all manner of subjects on the show, from Clarkson damaging a 30-year-old chestnut tree with a pick-up truck to the use of the phrase "ginger beer" for rhyming slang for "queer" (see 1).

19. Jason Dawe

The man they axed in favour of James May (or Captain Slow) in Top Gear's second post-relaunch series. He now writes about used cars. Oh, the glamour.

20. Video games

If tonight's episode isn't enough high-octane nonsense for you, there's always the chance to hear Jezza, Captain Slow and the Hamster on the latest Forza video game on the Xbox One. They are the official voices of the game.

21. Catch it on Dave

It might be the BBC's most bankable export, but it has also driven the success of Freeview channel Dave, where, if you were so tempted, you could watch the show at pretty much any time of the day or night.