SELF EMPLOYED CLIENT WHO EARNS £1440

That would depend on his other income

HMRC are going to require some statement of profit somewhere along the line.

Whether that's on an SA return or by SA is up to them.

Tssk! Why did HMRC pick Simple Assessment as a name when it has the same initials as Self Assessment?

Have HMRC asked for a return to be submitted ??
If he's registered with them as self employed (is he??) I would be surprised if they haven't

Yes, no, maybe.

It depends on whether he has any other income or not.
If he is receiving benefits then he needs to report his income even if it’s small.
Call HMRC self-assessment and tell them about his all income and they will be able to tell over the phone whether he is required to file a return or not.