Replying to zjab's non-sequitir:
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Contrary to the misleading implicit assumption of your comment, it is not in fact all that easy to become Prime Minister, and it is fairly difficult to return to the private sector afterward.
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Harry Truman's relative poverty is what forced the U.S. to face this problem half a century ago.
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Alternatively, consider Ulysses S. Grant - greatest military hero of his time, and two term president.  No pension.  Dying from cancer. Racing to finish his memoirs so that his family would be supported after his death, because he was, essentially, a pauper.
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More generally, it is usually difficult to win elected office at least twice and the job market for former MPs is pretty thin.  If someone has given up a career to run for elected office, I have no difficulty with their pension eligibility vesting after a short time, and the pension being fairly generous. 
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Otherwise only scoundrels would do the job, and we have more than enough of them, already.