Tax bill on zero hours contract

Alissas

Looking for some advice, my son has received a tax bill from HMRC to pay outstanding tax on a second job which was a zero hours contract where he was never taxed on his pay. The combined value of his day job and this second evening job has put his earnings above the personal allowance so he's paid tax on his day job but because he hasn't been taxed on his second one, he now has to pay that back in one lump sum. This is following this new Simple Assessment process. Should he have been paying tax on the second job and can we raise a complaint against his employer for not putting him on the correct tax on payroll? 
TIA

BikingBud

Did he advise:

• HMRC that he had 2 jobs so his tax code could be adjusted?
• The employers that he had 2 jobs?

If not then he is relying on the employers to use standard tax code and the crystal ball method of tax assessment which is somewhat ineffective and where tax can only be billed with hindsight.

From:https://www.moneyhelper.org.uk/en/work/employment/pay-and-tax-when-working-in-more-than-one-job

Example 2: two jobs below the Personal Allowance

Richard has two jobs. His main job pays £10,000 a year and his second £9,000.

Both of these are below the Personal Allowance, so he can split his allowance between the two jobs.

He can contact HMRC and get them to transfer £2,570 of unused allowance from his main job to his second job. Or he can wait until the end of the tax year, and ask HMRC for a refund.

You should only ask for your Personal Allowance to be split if your income from each job is predictable and stable. If it’s not, and one job ends up paying you more than expected, you’ll have underpaid tax.

Tax codes for second jobs

It’s important to check your tax codes. This will help make sure you’re paying the right amount of tax and don’t get unexpected tax bills, penalty charges and interest.

Your main job, assuming it pays you more than the Personal Allowance, should be 1257L for the 2023/24 tax year.

Your second job should have a BR, D0 or D1 tax code, depending on whether or not it’s taxed at the basic, higher or additional rate.

You can find your tax code on your payslips.

You can tell HMRC about starting a second job using the new starter checklist from your new employer.

Given the above, as a zero hours contract is neither predictable not stable, I would offer that this was reasonable way to operate and should have been expected.

What about NI payments?

National Insurance on second job

If you earn above £242 a week in the 2023/24 tax year, you’ll have to pay Class 1 National Insurance contributions.

If you earn more than this in both of your jobs, you’ll pay National Insurance contributions on both jobs.

chrisbur

Was a starter checklist offered for completion by the second employer.
If so was option a b or c selected.
If c was selected the employer should have taxed all earnings at basic rate.

However to be honest even if the employer was at fault it is very unlikely that complaining will help in any way and may mean he does not get any future work with them.  
The tax will have to be paid though he might be able to spread it out if he contacts HMRC.

https://www.gov.uk/guidance/starter-checklist-for-paye