Norwegian have a number of leased long haul aircraft operating for them from Gatwick currently. Don’t know if any of these are in an all white livery though: https://www.routesonline.com/news/38...atwick-in-s19/

To bring this back to BA, I do think this puts them in quite a competitive place on NYC and Orlando from Gatwick. The BA Economy Basic fares are usually in the same ball park as Norwegian but include improved free food and drink and are largely on densified but refurbished 777s with good IFE, WiFi etc which in my view is going to be superior to some of these leased in aircraft.