iPad USB power in LGW 747

I'm flying to LAS from LGW in September in PE and i've read that there's no charging allowed. But what not clear is if the seat back USB provides enough power to keep the iPad charged if plugged in ?
I will have a iPad 3 with the Apple USB cable and a Wi-Fi hard drive

Seek and ye shall find.

forum/index.php?f=4&t=279027&p=838979&hilit=USB&rb_v=viewtopic#p838979

[buns]

Having just got off a Gatwick 747 (travelling in PE) I found plugging in the USB charged my I Phone happily enough, but not my I Pad

buns

I will have a iPad 3 with the Apple USB cable and a Wi-Fi hard drive

It might be worth checking out if you can actually use your Wifi Hard Drive during the flight.