BRITISH STYLE ROMAN BLACKWOOD
The Roman Blackwood conventional method, as devised by the successful Blue Team Club of Italy, proved to have a flaw in the responses in so far that the response of 5 Hearts was ambiguous. Each of the other three responses are without ambiguity. In the case, as an example, that the Ace-asking partner receives the response of 5 Hearts, then the Ace-asking partner, holding the Ace, for example, expects the responder to hold the Ace and a second, unspecified Ace.
It is this ambiguity or flaw that the British-style Roman Blackwood variation addresses. In order to overcome this inconsistency, this variation added an extra response to clarify the response. The responses are shown below. Source: oeb
Shows 0 to 3 Aces.
Shows 1 or 4 Aces.
Shows 2 Aces of the same color, / or /.
Shows 2 Aces of the same rank, / or /. 5 NT: Shows 2 Aces of dissimilar or unlike color and rank, or / or /.
In the case that the first response of the responder to an Ace-asking 4 No Trump is 5 No Trump, then the partnership really has no normal way to ask for Kings. However, the partnership may use any other, additional conventional method to ask for Kings, which means the employment of a second conventional method singly to ask for Kings.
Since it has proven to be more effective in judging the possibility of a grand slam to know the the location and/or identity of a specific King, some partnerships have agreed to employ a different approach if the normal response would be 5 No Trump. The partnership agrees simply to employ the bid of 5 to show two Aces and no additional values, and employ the bid of 5 to show additional values and strength.
Since the Ace-asking partner is able to infer from the Major suit responses that the responder should have bid 5 No Trump, then the Ace-asking partner has the communicated information that the two Aces are of dissimilar color and rank plus the additional information about the held values.
The Ace-asking partner is able to infer the correct conventional bid by receiving contradictory (or incorrect) information from the responder, and will bid accordingly. It must also be noted that the partnership may benefit from agreeing to employ two different conventional methods, one for the Ace-ask and one for the King-ask.