HMRC Self Assessment tax return late filling fixed penalty of £100

Hi. I am stressed and worried. I am planning to apply for British Citizenship. I am posting on this forum hoping that somone who applied for British Citizenship in similar situation could share their experience or direct me to further resources to read. I will appreciate any advise on the matter described below.

Four years ago I forgot to fill Self Assessment tax return on time. I incured an automatic late filling fixed penalty of £100 and received a penalty notice. I paid a penalty, filled Self Assessment tax return and the matter was closed. No court involved. I have been living in the UK since 2010. I have been employed most of that time and some time ago I also registered for self assesment to carry on as self employed additionaly to my full time employment. I am EEA national. I obtained blue card (Document Certifying Permanent Residence in the UK). After Brexit I applied for Indefinite Leave to Reamain and was granted ILR. Besides that one penalty I have good, clean record (no other penalties, no fines, no convictions). I also contributed to the community as volunteer.

I read a lot on the Internet. I found contradictory informations. Some people state that if penalty was paid and no court was involved then there is no need to declare it on application form. Other people suggest to write a separate cover letter with explanations. However on Form AN: guidance (accessible) - GOV.UK clearly statement is made in section 10.1 Criminality that:

"You should also include any out-of-court disposal such as a fine, a caution, a warning or reprimand, a community sentence, a civil order, a civil penalty, a civil judgment, a hospital order or a restriction order. All fiscal fines must also be disclosed. If you are not sure, you should declare all penalties or orders.
Fixed penalty notices such as those issued under the coronavirus Regulations, or for traffic offences such as speeding or parking tickets must also be disclosed, although will not normally be taken into account unless you have failed to pay and there were criminal proceedings as a result, or you have received multiple fixed penalty notices in a short space of time."

https://www.gov.uk/government/publicati ... accessible
https://www.gov.uk/government/publicati ... -character

Some people on the Internet suggested that failure to pay tax or submit returns on time can be considered a breach of UK tax laws and may impact the "good character" requirement. However other source states that: Missing the deadline for submitting a Self Assessment tax return and incurring a £100 penalty is not considered a criminal law break, but it is a violation of tax regulations set by HMRC.

I also read that: If you have a non-custodial sentence or a caution, you must wait three years from the date of the conviction or caution before applying for naturalisation as a British citizen. However, if you have a custodial sentence of 12 months or more, your application will likely be refused regardless of the time elapsed.

I also found this about fixed penalty notices on the:

https://www.gov.uk/government/publicati ... -disposals

8. Non-custodial sentences and out of court disposals

This page describes the types of non-custodial sentences and penalties a person may receive and explains how to consider these when deciding an application.

8.4 Fixed penalty notices - penalty charge notices and penalty notices for disorder

Fixed penalty notices, penalty charge notices and penalty notices for disorder are imposed by the police or other authorised enforcement officers for traffic rule, environmental and civil violations. They enable the criminal justice system to dispose of certain minor offences without the need for a person to attend court and do not form part of a person’s criminal record.
A fixed penalty notice will not normally result in refusal unless the person has failed to pay or has unsuccessfully challenged the notice and there were subsequent criminal proceedings resulting in a conviction. In such instances, they should be treated in line with the sentence imposed by the court.

https://www.gov.uk/government/publicati ... -disposals

The penalty was issued four years ago, so could it be considered as lapsed, because there is three years bar relates to conviction or caution? Could this penalty considered as not meeting a good character requirements and or financial soundness requirement?
Can I be refused British Citizenship because of this one penalty on a base of violation of tax regulations set by HMRC?

Has anyone of you have experience or more knowledge about this kind of matter? I would appreciate any insights or advise on this matter. Kind regards.

If you've dealt with your tax affairs in a proper manner generally then an odd fine will have no impact on your "Good Character". It's a fact of life, happened to me, cleared up everything, never disclosed it anywhere. If it it makes you feel better attach a note about this, explaining the circumstances concisely - you don't need to prove anything. It will be ignored.

Just declare it. PCNs don't need to be declared if paid, but FPNs are different and (slightly) more serious. You only had one and you paid it nso unlikely to be a problem if you declare it.