chaika,
We insist that the meeting should be held as soon as possible. or We insist that the meeting be held as soon as possible.
The first example (with should be held) is said in that book to be use in BrE and the second one (with be held) in AmE.

It seems to me that I've understood what confused me.
For example, If I had more time I should learn Japanese. Here should has the same meaning as would. That is, it would be possible to say If I had more time I would learn Japanese.
In We insist that the meeting should be held as soon as possible, should has another meaning, but I thought that the same as one above.