Is the loss of money on the game more than what it would cost for a lawyer if you did loose your case? If not, it's better to just cut your losses.

If you did not 'register' this game ideas as your own, you really can't do much in court.(as far as US court goes, not sure how UK or wherever's court operates.)

You have to remember, you can design products to specs taken from another product, but you cant design them with parts taken from another product.