It sounds like both British Airways and Virgin Atlantic are bringing some chargers to the gate area. However, we’re guessing that there’s now going to be quite the demand for electricity, so maybe even pack one of those travel extension cord things—the more plugs the merrier.
If your device doesn't have enough juice to switch on at boarding there’s still hope, as it sounds like the two aforementioned carriers are even stepping up and offering to ship and stow your device to you. No need to toss that brand new cell phone in the trash.
Bottom line is that the demand for charging things up at the airport will soon be more than ever, so just do your best to keep things ready to go. Otherwise add in a little extra time to search out an open outlet.