Speed of registration as self-employed for once-a-year job?

Waking_Up

Not sure this is the right place, but here goes:
For the last 9 years I have done an annual translation job for an acquaintance, once a year. They have paid me for the service, amounts ranging from £200 to £500, depending on the size of the job. Year to year, I have not known whether I would be asked do another job, so foolishly haven't bothered to register as self-employed, nor paid tax on any of this income as it seemed like an insignificant one-off payment, and I was not trying to find more of the same kind of work. However, the most recent job came to £1500 which feels like a significant sum. I am not undertaking any other work of this kind for this acquaintance or any other 'clients', this is an annual one-off.
This time, the fee is being paid by a 3rd party abroad who is funding said acquaintance. They want my company name and 'number' in order to pay me, presumably thinking that I am a regular commercial translation service. How quickly can I get registered as self-employed (there's a funding deadline to meet) in order to obtain the kind of official status they require, and (eek) what is the backlash likely to be in terms of tax on previous years' earnings? I feel like such a disorganised fool. I have looked at the HMRC website but it doesn't say how quickly they get back to you with your 'business number', which is what this 3rd party is requesting, sharpish (as in tomorrow, we have just found out!).
I also have a regular job, earning £18K pa, I imagine this will have some bearing on any tax implications.
Any advice gratefully received!

Dazed_and_confused

Have you ever needed to complete a Self Assessment return for any reason in the past?

Waking_Up

Thank you for taking the time to respond
I was self-employed briefly (3 years) in the fitness industry some 15 years ago, but I set that up with the help of an accountant so have little recollection of how it worked, apart from it involving many regular payments from many clients, not just this strange annual one-off scenario. When I retrained in my current profession I 'closed' my self-employment.
Are you saying this could be significant?

Andy_L

You can register as a sole trader in only slightly longer than it takes you to think up a company name. You just need to register for self-assessment, there is no formal registration of the company with companies house and no number issued

https://www.gov.uk/set-up-sole-trader

Dazed_and_confused

Are you saying this could be significant?

Yes. Unless you have been made bankrupt you keep the same reference number for Self Assessment forever. So when you register again HMRC will simple re-open your existing Self Assessment account.

So you may be able to find this reference (known as a Unique Taxpayer Reference, UTR for short) on existing papers you hold. Or by logging into your HMRC Self Assessment account.

You still need to register with HMRC but the number you need urgently already exists (unless you have been made bankrupt).

Waking_Up

Thank you, Andy, and thanks again, Dazed!
No, no bankruptcy, just retraining. That is really reassuring, now I just need to find that UTR, by the sound of it. My accountant did all my tax returns, can I still access my HMRC self-assessment account online somewhere?

TheCyclingProgrammer

I would argue that a one off job once a year does not make you self employed as you aren’t really trading.

That said the income is still taxable and should have strictly been declared. If you already did a self assessment I would say you should enter it in the “other income” box.

It may be simpler to simply inform HMRC of the extra income and ask if they can adjust your tax code.

For the client asking for your “business number” just tell them you are a private individual and not incorporated.

Waking_Up

Thank you, The Cycling Programmer!
Yes, I do want to put it right retrospectively. The most recent sum is, at least for me, a significant amount of money, and it brings the whole tax issue sharply into focus. I have just been trying to access my old self-assessment account on the HMRC website, using my NI number, to no avail, so I will do as you say, and tell the client I am a private individual and hope this will suffice, and contact HMRC in the meantime and ask them how they think I ought to proceed. It would be galling if they were unable to pay me on account of not being a registered company.

Dazed_and_confused

You may want to read up on the £1,000 "traders allowance" which applies from 2017:18.

That may help you decide how best to approach this with HMRC.

If the "acquaintance" is related to your main employment it may complicate matters but in principle it is something which could be applicable.

If the most recent work (£1,500) was for the 2018:19 tax year then it could in theory help you with two tax years and may mean there is no extra tax to pay for 2017:18 and less than you imagine for the current tax year.

Andy_L

There is (since 2017) a tax free allowance for the 1st £1k of self employment earnings as a "trading allowance" If you're gross income is below that you don't even need to register as self-employed

https://www.gov.uk/guidance/tax-free-allowances-on-property-and-trading-income

Waking_Up

Thank you both, Dazed and Andy!
The translation work is altogether unrelated to my job, it was something I started doing as a favour for a friend of a friend.
I am waiting to hear back from the organisation which is responsible for funding this most recent piece of work, to see if they are able to process a payment without all the information they require, such as a 'business number' while I contact HMRC. The trading allowance may not apply though, as I already earn a PT salary in mt professional role. Will look into this. Thanks again!