By Ed Warner Sir Jim Ratcliffe’s minority investment in Manchester United is fraught with pitfalls for the British billionaire, writes Ed Warner. Imagine for a moment that you’ve set your heart on buying a stately home in desperate need of repair and have the cash to do it. You’ve lined up your tame kitchen designer and chosen the curtain fabrics. At the last minute the selling family calls to say they’ve decided to stay put, but that you are welcome to buy a quarter of the property – say, the stable block they keep their thoroughbreds in, which does come with staff accommodation. Are you inte…