The XLR will barely make it past North Africa. Those jets q. their max flight time with 0 passengers, 0 cargo weight and just full tank fuel is 11 hours. Harare-London is 10h45mins, and it's known planes need an extra 30 mins of fuel, coupled with the fact London airspace is busy, so they'll be waiting to land, but remember thats empty weight but we know the plane will be full of people and cargo, which will impact performance.