Scottish Daily Mail
South ♠ Q 10 9 8 ♥ AK7 ♦ A72 ♣ J64 You open 1NT (12-14) and your partner responds 3♠. What do you bid next? How often do you hear a forcing response to your NT in your best suit and when you’re absolutely maximum? Very rarely, so you must be careful not to waste the opportunity by merely bidding 4♠ — you would do this with a spade less and ♥J instead of ♥K.
3♠ is a strong bid; tournament players today use it even to show slam interest, as they have other means (via Stayman or Transfers) to show lesser hands.
This is the time for you to use an advance cue bid, which should be perfectly acceptable (even in social rubber bridge circles), because it is a common-sense bid.
when you now bid 4♦, you are agreeing spades as the trump suit and showing maximum strength with the ♦A.
This cannot logically be a natural bid, because you have already limited your hand and, without spade support, you would surely have rebid 3NT. The message to partner is that, if he is interested in a slam, so are you.