Why not floo instead of thestral to London?

[a_reader2003]

No: HPFGUIDX 91564

Is anyone else as irritated as me that Harry and Hermione didn't just 
floo out of Umbridge's office straight to Grimmauld Place, instead of 
wasting all that time being caught and riding thestrals to disaster 
in the MoM ?

Hermione and Harry had a clear 5 min before Umbridge came stampeding 
back to catch them; plenty of time to whisk into the fire. Even with 
Kreacher pretending Sirius wasn't there, you would have thought it 
would have made Harry mad enough to just walk straight into the fire, 
as it would have got him to London faster than anything. From 
Grimmauld place he could have got the tube...

Yeah, yeah, I know, it was a plot device to ensure Neville, Luna and 
Ginny got there too for reasons we will no doubt discover, but clunky 
or what..

Carolyn, grumpily.