There is no specific law, but it is covered either by the Protection of Animals Act 1911 or the Animal Welfare Act 2006 (don't recall which), but they prevent any sort of unnecessary suffering to an animal.
But from a purely practical point of view, have you ever tried to do this to a cow? Its an urban myth of that I am sure. If you have ever tried to make a cow move (forwards, backwards, sideways or otherwise)? Unless it decides its going to it won't. I should know I was brought up with them (that is a reference to the fact of being brought up on a farm, not to my sister).