Only issue I can think of would be like the problem with cannards or bull bars, because of the whole 'dangerous to pedestrians' thing... Doubt anyone would be keen on getting bonnet'd by something that has a tow hook sticking out of it.
Doesn't seem to be anything to actually make it illegal though, and you'd be ridiculously unlucky for anyone to question it as it's there to tow the car by, and it will have been intentionally put there which excludes you from most stuff as it's a specific modicfication, not damage or what-not. Go for it man, it'll be fiiine.