As the highest one level bid the 1NT overcall is very inconvenient. And such intervening bids also cancel out quantified bidding.

In this next sequence East’s 1NT intervention means he has 15-17 points, a balanced hand and a stop in North’s ♥s. So what should South do? With a good spade suit and support for ♥s he might have planned to bid 1♠. But now he can’t do this over the 1NT intervention.

Besides, the bidders, North and East, have so far accounted for a minimum of 28 of the available points (North’s opening one of a suit promises 13-19 points and East’s overcall of 1NT promises 15-17 points). So South and West cannot have more than 12 points between them. With less than 6 points South will not bid:

North	East	South	South's points
1♥	1NT	No bid	0-5

But with higher values, South should bid as follows:

North	East	South	South's points
1♥	1NT	Double	6-11 (unbalanced)

If vulnerable South is likely to pass as he needs at least 11 points for his double bid. This is because he stands to lose more points when vulnerable, so he needs the stronger hand to back his call.

In the next example, South’s 2NT overcall over East’s 1NT opening bid would normally mean 16+ points. But since North has already opened one of a suit, the response overcall can be made with less points, in the 10-12 range. However, South must still hold a balanced hand:

North	East	South	South's points
1♥	1NT	2NT	10-12 (balanced)

In the case of no trump replies to an opening bid of 1NT, the quantitative responses have to be modified if there has been an intervention. With no intervention South promises a balanced hand and the normal point range:

South points with no intervention
North	East	South	South's points
1NT	Pass	2NT	10-12
1NT	Pass	3NT	13-18

But with the intervention, South needs to adjust his values (and show a stopper in the intervening suit bid):

South points with intervention
North	East	South	South's points
1NT	2♥	2NT	11-12 (and a stop in ♥s)
1NT	2♥	3NT	13+ (and a stop in ♥s)

Coping with intervention – summary

Response with no intervention
North	East	South's response	South's points
1♥	No bid	2♣	9-15
1♥	No bid	1NT	6-9
1NT	No bid	2NT	10-12
1NT	No bid	3NT	13-18
Response with intervention
1♦	1♥	1♠	6-15
1♦	1♠	2♦	9-15
1♠	2♣	2♠	6-9
1♥	2♠	3♥	8-10
1♠	2♦	3♠	10-12
1♥	1♠	2♣	12-15
1♥	1♠	1NT	6-9
1♥	1♠	2NT	10-12
1♠	2♥	2NT	10-12
1♦	1♥	3NT	13-15
1♥	1NT	No bid	0-5
1♥	1NT	Double	6-11
1♠	1NT	2NT	10-12
1NT	2♥	2NT	11-12
1NT	2♥	3NT	13+

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To continue reading go to: Intervention over Astro

By Nigel Benetton – based on the UK Acol Bridge Bidding System
Last updated: Wednesday, 12th May 2021