There were 5 guineas coins minted up to 1777, 2 guineas also to 1777 (patterns only), 1 guinea to 1813, half guinea to 1813, third guinea to 1813 and quarter guine minted only in 1718 and 1762. Sovereigns superceded the guinea and were minted from 1817. In Victorias reign and Edward VII and George V sovereigns were minted in the colonies as well as by the Royal Mint. 1918 sovereigns were not minted in this country they were minted in Canada, India and Australia and were meant for use only in these colonies but some did turn up in England and were considered legal tender. You can tell where they were minted by looking for a small letter on the reverse useally somewhere just above or below the date. 'C' is the Ottowa mint, 'I' Bombay, 'M' Melbourne, 'P' Perth and 'S' Sydney. The value of the coin will depend upon int condition as these coins are collectable and thus if in good condition will be worth more than the bullion value. I suggest you look up to see if there are any coin dealers in your area and take it to them to be valued.