An article of newspaper ????

Lew said that at the end of June last year,
just before he took office,
he advised Leung to identify the three professionals
should the pan-democrats keep harping on the issue.

這是寫法上的拆解

你問的should 意思 「假如」pan-democtate(泛民派人) keep (持續) harping (重提)...意思如同if，但用should是指不確定的假設和用預計的角度來講。在所有危機處理或考慮可能發生事故的對應方案寫法都會用should(if) X happens, take action A；should(if) action A fails, take action B...

由於要把多個層次的情況寫入同一句，這是報紙常用的不按太傳統文法組句。

因為..

...he advised Leung that should pan-democrats keep harping on the issue, he should (ought to) identify (give out the identity of ) the three professionals.

才算較會詳細的句子。

這只不過是假設法的特殊用法罷了！只是將假設法的if省略了，但這種省略得注意，必須將動詞放在主詞前面。

如：

Should it rain tomorrow, I should stay at home. = If it should rain tomorrow...
(萬一明天下雨，我將留在家裏）

Were I a king, I should not be able to do it.= If I were a king,.....
（即使我是國王，我也不能做它。）

Had I known your address, I should have written to you.
= If I had known your address......
（要是我知道你的地址，我就已寫信給你了。）

所以，你所引的句子，其意思是：......he advised Leung to identify the three professionals if the pan-democrats should keep harping on the issue.

他建議梁去確認那三位專業人仕，萬一汎民在這議題上死纏不放。


希望幫到你！