I'm trying to catch any possible errors arising from a SQL UPDATE (such as a duplicate key value) so that I can display a custom error message. I've tried the following code without success - even when the update fails the standard warning appears and 'Error' never gets printed in the console.

Is what I'm trying to do possible?

Not currently, no. fpmi.db.runUpdateQuery catches errors internally and displays them. I've taken the liberty of moving this thread to the feature request forum.

This has been changed in Ignition - all database errors can now be caught and handled via Python exception handling.

That's great

Just to prove users are never satisfied - is there any way you can trap a SQL error number from the database?

You mean how to pull out details of the error that you've caught? You can catch the exception and learn about its cause like this: