Extra legroom in economy on LGW and MAN routes

Apologies if this has been asked before; I don't get on the forums much these days. I came across this on VA's website via a link from a Flying Club email. Can anyone tell me any more? Where will these seats be located? Have they already been fitted? How much will they cost?
Passengers flying in Economy now have the option of purchasing an Extra Legroom Seat on all 747 flights from Gatwick and Manchester. These spacious seats will be fitted on each aircraft, offering those passengers who prefer a little more room, the choice to stretch their legs at a little extra cost.
The seats will be sold on a first come first serve basis at the check in desk on the day of departure so arrive early to avoid disappointment.
Passengers flying in Economy now have the option of purchasing an Extra Legroom Seat on all 747 flights from Gatwick and Manchester. These spacious seats will be fitted on each aircraft, offering those passengers who prefer a little more room, the choice to stretch their legs at a little extra cost.
The seats will be sold on a first come first serve basis at the check in desk on the day of departure so arrive early to avoid disappointment.