Complex sentence: The publication of the letter ensured the subsequent electoral defeat of the Ramsay MacDonald-led Labour Government, and it has been suggested that MI5 or MI6 may have been involved in leaking the forged letter.
Split into simpler sentences: The publication of the letter is thought by some to have had an effect on the subsequent electoral defeat of the Ramsay MacDonald-led Labour Government. It has also been suggested that MI5 or MI6 may have been involved in leaking the forged letter.