I've just done some searching on internal systems and newsletters.
By the looks of it, it is available on French, Spanish, Swiss, Portugese flights as well as Gatwick and Bristol flights.
As far as I can tell, it is not a replacement for hold luggage, but merely a expeditious and convenient method to get your luggage at your arrival airport quicker.
"HANDS FREE
Following the very positive uptake of Hands Free in France, Spain, Portugal, Switzerland and Bristol, with good feedback from both our customers and the Ground Crew, we will now offer all customers departing LGW the opportunity to upgrade to the Hands Free experience.
With Hands Free, customers travelling with or without a hold bag can drop off their cabin bags at Priority Bag Drop to be placed in the hold. For a small fee, all their bags (including hold bags if any) will be marked as priority and then delivered fast at arrivals, before anyone else’s. With this, customers will also enjoy a hassle-free experience at the airport (no need to unpack at security and carry a trolley bag through the airport) and will enjoy priority boarding (right after Speedy Boarding).
Prices are £4/€5/CHF6.- for an individual or £10/€12/CHF15.- for a group of 3 to 6 people (“Family Bundle”)."