This is assuming you put your camera with your heavy telephoto lens on the tripod and then you carry the whole lot resting on your shoulder and you walk all over the places, as if you're playing soldier and you think your tripod and attached camera is a rifle. If you want to move a little over there to get a better viewpoint, then that's fine if you do that, but if you're going to hike hundreds of yards somewhere else between each few shots, then it makes senses to take the camera off the tripod and carry them in each hand. Photographers at football matches who have monopods to support heavy fast telephoto lens would carry it like a rifle just to make a small jog down the sidelines to get a better viewpoint but I don't think they would do that all the way back to the car after a match.
It makes sense to just take the camera off the tripod and carry both, and if you find it annoying to unscrew the camera off the tripod then have to screw it back on, then you could buy tripods that have quick release system that you can screw a plate on to the camera, then just click it to the tripod head. (You could order spare parts and attach to different cameras or heavy telephoto lenses, so it is quicker to change them than to unscrew one and then screw on another.) Release the camera from tripod, go somewhere else, attach it. It offers the option of just drop the tripod and handheld your camera. Beside, chances are you would have to carry your camera bag anyway, so makes senses to use that sort of quick release system so you can just take camera off tripod and carry them by hand and carry bag over shoulder than to carry bag over one shoulder and the tripod with attached camera over the other shoulder.
But well, if you would still prefer the item you found on the Internet, you could check their website, look for details to see if you can buy it and get it shipped to the UK, sometimes you can order something online if it happens to be overseas, as long as those are allowed items.
