modeller, I disagree with you vehemently. I was living out there and mucked around with many of the influentials of the Colony (the Government and indeed the House, the Press and the FCC, industrialists both Chinese and foreign.
Thatch thought that HK was indefensible against the might of China and, yes, she was right in that. However, what she or the FO in briefing her, under-estimated the desperate want of the mainland to be in a position to see Taiwan accede to their influence. (Still there).
If she had pushed for a model along the lines of Monaco and France, and using the "sell" that it could snare Taiwan, they may have pulled it off.
By the time Patten arrived, it was too late. He was dealt a bad hand of cards like Soames with Rhodesia and even Mountbatten over India (more obtuse there). What did the FO do, and the real killer, was to appoint a plonker like Lord Caithness to the FO's job of HK responsible; he was known to us as Lord "Scrotum" - totally useless and lacking any sense of creativity and diplomacy of such a more productive route.
The question is was it deliberate and what was the wider hegemony in play between the USA (West) and China?