There has been some concern about what the penalty regime would be for RTI.
It seems that up to April 2014 at least there will be no penalties for late/innaccurate RTI submissions to HMRC, other than the "Final Payment" of each year, for which the penalty regime will be the same as the one currently operating for P35/P14. (which seems logical enough, though lets hope the letters go out before September 2014!)
That may change in the future, but at least we're not *starting* with a CIS-like penalty regime.
EDIT: Just to clarify, there can be penalties for innacuracy leading to underpayment, as in the current regime where an inspection discovers significant error, but such penalties are mitigated as before by voluntary disclosure and honest and competent attempts to comply.