Sole Trader or Box 16 "Other UK Income"

[bins]

My wife is about to retire from teaching and, when retired, is considering doing a one-off teaching-related consultancy job for the local education authority - probably around 20 days work over a 3 month period.

Does she need to register as a sole trader, pay Class 2 NICs etc? Or can she simply enter the income and (minimal) expenses as "Other UK Income" using Boxes 16, 17, 18 & 20?

I've trawled the HMRC website but darned if I can find any relevant guidance - any suggestions where I can look?

[Tax Champion]

If this is a one-off with earnings below the "small earnings" limit of £5315, you can just show it as "other income" - there are no NI implications, and for such a short period there would be no need to do anything more.
However if there will be further work, or if her income will be more than this, she should register as self-employed and do things properly.

[bins]

Thank you, Tax Champion.

Her earnings will be above the "small earnings" limit of £5315 so looks like she will have to register as a sole trader.