English for Today by Ganiu Abisoye Bamgbose (Dr GAB)
TO STAND UP or TO BE UPSTANDING
The new members were asked to ~be upstanding~ for a while (nonstandard).
The new members were asked to stand up for a while (standard).
To be upstanding is to behave in a morally acceptable way: He is a decent upstanding young man. ✔️
Note, however, that to be upstanding can mean “to stand up” in American English.
Also, in British English, to be upstanding can be a direction to all persons to rise to their feet before the judge enters or leaves the court, and also a direction to all persons present to rise to their feet for a toast at an event:
Shall we be upstanding to celebrate the couple. ✔️
GAB