Link to short story that JKR wrote for charity is n...

[Zara]

> Magpie:
> Don't James and Sirius go stiff in that bird-dog way when they see 
them 
> too? I assumed this was them dealing with Serious Business.

Zara:
Representatives of the Ministry, that is, fully qualified adult 
wizards, would be serious business compared to dealing with Muggle 
police. They might, actually, be able to *do* something to Our 
Heroes, rather than standing around being fat, ignorant Muggles it is 
amusing to poke fun at until one tires of the game.

> Sandy:
> I like this interpretation better than any other I have read and 
think it is
probably in the correct vein. I do try to keep in mind how young they 
all
were when they joined the Order, and how young James and Lily were 
when they
died, but this sounds like a Marauders prank to me. I feel that if it 
were DE's
chasing them they would have had no qualms about AKing the policemen 
on the
spot. 

Zara:
Why thank you! You surmised correctly that I was jesting, but you 
make a good point. (Though I would still say the smart money is on  
Rowling writing the scene imagining Death Eaters or other Voldemort 
supporters on the brooms.). 

If they were DEs, they were dumb DEs. To AK anyone, they might need 
to have come close enough for Our Heroes' defense to work, but a trio 
of Reductor or Blasting Curses launched at the cars/cops/boys from 
the end of the alley before swooping in for the kill would have been 
sensible. Unless, of course, avoiding damage to the cops was a 
consideration of the people on brooms, which would certainly not 
apply to Death Eaters.