Question: Please explain the Drury convention and its modified version. In what position and with what types of hands this convention is applied?
(Zafar ul Haq, Karachi.)
Answer: The Drury is a useful convention strictly to be applied when the partner opens the bidding in a major suit in the third or fourth seat. His partner, who has already passed, applies Drury Convention to ascertain whether the opening bid has been made on full or minimum value provided he has good support for the major suit and has with 10 to 12 points count.
The convention invented by the late Douglas Drury for responding to third and fourth seat major suit opening bids with a bid of artificial two clubs, which is unconditionally forcing. With a subminimum opening bid, opener must rebid two diamonds (artificial), after which responder can sign off at a low level of two in one of the major suits. With a sound opening bid, opener may make any other rebid, which would ensure a game contract with a 90 per cent chance.
As further explanation of the Drury convention is that the two clubs response to a third or fourth-hand opening bid of one of a major suit is known as simple Drury. The two clubs response is an artificial bid and merely asks the opener whether or not he has a full opening bid.
If the opener has a subminimal hand, he rebids two diamonds. If he has full values for his opening, he makes any other appropriate rebid. If opener has a full opening bid and other suit being diamonds, he can either jump to three diamonds, if his hand is very distributional, or he can temporise with a two diamonds denial and later either bid diamonds naturally or rebid two no-trump.
To use the Drury convention, the responder should have a ten to twelve points hand. For example, if the responder held

[A]     S KJxx     H xxx     D AQxx     C Jx

opposite a third or fourth-hand opening bid of one spade, he would bid two clubs, Drury. The opener might hold any of the following hands:

[B]     S AQxxx    H Jxx     D KJ      C xxx
[C]     S AQxx     H AJxx    D Kxx      C xx
[D]     S A10xxx   H AJ      D KJxx     C Kx
[E]     S AQxxx    H x       D KJxxx    C Ax

After the auction

Opener     Responder
-               Pass
1S                2C

The opener would bid two diamonds with Hand B, having less than a full opening bid. The responder would then sign off at two spades. With Hand C, the opener would make his natural rebid of two hearts. With Hand D he would rebid two spades, planning to rebid diamonds naturally at his next turn. With Hand E opener has uneven enough distribution to jump to three diamonds.
The responder might also hold a hand such as

[F]    S Kxx     H K10xx     D Axxx     C Qx

with Hand F opposite Hand C above, the Drury convention makes it easier for the partnership to find his 4 - 4 heart fit. If Drury were not being used, responder would probably have contented himself with a jump raise to three spades.
If responder holds a hand such as:

S x    H xxx    D Ajx    C AJ10xxx

he would bid two clubs over his partner's one spade opening, and rebid three clubs over whatever the opener rebid:

Responder   Opener
Pass            1S
2C      2D, 2H, 2S
3C
    Modified Drury

The Drury Convention allows a responder who is a passed hand but who holds 10-12 points and support for his partner's major suit opening to bid two clubs to ask his partner whether the opening bid was based on full opening strength. As originally designed, the Drury Convention required opener to rebid two diamonds if his opening bid was of subminimum strength. Other rebids showed full or extra values.
More modern use of the convention, called "Reverse Drury," that requires opener rebid his suit if his strength is less than that of a full opening bid. And bid two diamonds (artificial) to indicate full opening bid For example your partner passes in the first seat, Right Hand Opponent also passes and you open one heart in the following hand:

Partner      You     Your hand is.
Pass         1 H           S A10 8
2 C          2 D           H AQ976
                               D J
                           C K1096

In addition, whereas the original design of Drury allowed responder to show a real club suit, rather than support for opener's major, eg, a hand such as:

S xx     H xx     D Qxx    C AQJxxx

by responding two clubs and rebidding three clubs, modern treatment requires responder to jump to three clubs directly with such a hand (No way a strong hand).
There are two principal advantages of these modifications. First, opener's rebid of two of his major suit, rather than of two diamonds, to show weakness makes it somewhat more difficult for the opponents to enter the auction. Second, the restriction of responder's two clubs response to hands containing good support for opener's suit allows more efficient slam exploration when opener has better than a full opening bid in the range of 19-21 High Card Points count.
Note: Reverse Drury does not apply if the major suit opening is either overcalled or doubled by the Left Hand Opponent. If the Right Hand Opponent doubles 2 clubs response by your partner, you can proceed with bidding according to convention.
CORRECTION
In the Bridge Notes column last weekend edition, the final bid of 7 spades was wrongly indicated with a symbol of club suit instead of spade suit. The error is regretted.