Mike Gunn wrote:
That would seem to be sensible, but it doesn't appear to be what is suggested in the document I have just downloaded from the FIDE website
In Appendix 3
A.4.2.1 If the arbiter observes an action taken under Article 7.5.1, 7.5.2, 7.5.3 or 7.5.4, he shall act according to Article 7.5.5, provided the opponent has not made his next move. If the arbiter does not intervene, the opponent is entitled to claim a win, provided the opponent has not made his next move
So what happens if no arbiter is present? That seems to imply a player can claim.
7.5.1 to 7.5.4 extend the definitions of illegal moves to the downright silly.
7.5.1 An illegal move is completed once the player has pressed his clock. If during a game it is
found that an illegal move has been completed, the position immediately before the irregularity shall be reinstated. If the position immediately before the irregularity cannot be determined, the game shall continue from the last identifiable position prior to the irregularity. Articles 4.3 and 4.7 apply to the move replacing the illegal move. The game shall then continue from this reinstated position.
7.5.2 If the player has moved a pawn to the furthest distant rank, pressed the clock, but not replaced the pawn with a new piece, the move is illegal. The pawn shall be replaced by a queen of the same colour as the pawn.
7.5.3 If the player presses the clock without making a move, it shall be considered and
penalized as if an illegal move.
7.5.4 If a player uses two hands to make a single move (for example in case of castling,
capturing or promotion) and pressed the clock, it shall be considered and penalized
as if an illegal move.
7.5.5 says what happens next
7.5.5 After the action taken under Article 7.5.1, 7.5.2,7.5.3 or 7.5.4 for the first completed illegal move by a player, the arbiter shall give two minutes extra time to his opponent; for the second completed illegal move by the same player the arbiter shall declare the game lost by this player. However, the game is drawn if the position is such that the opponent cannot checkmate the player’s king by any possible series of legal moves.
So read the small print !
On the face of it, it's entirely arbitrary as to whether an illegal move loses as it depends on both the presence and intervention of an arbiter.
If you want to outlaw two handed castling and not placing a Queen after promotion and penalise pressing the clock without moving, wouldn't a simple two minute penalty suffice?