For a long time, HMRC have taken the view that where the law allows a "reasonable excuse" for the late filing of a return --- be that a self-assessment personal tax return, Corporation Tax return, VAT return or PAYE return --- the reasonable excuse must relate to an event or situation that was exceptional and unforeseeable. Ordinary failings or misunderstandings were not enough.
We are definitely seeing, however, a change in attitude from at least one Tribunal judge. In Colin Humphreys v Revenue & Customs  UKFTT 98 (TC), the tribunal said (at para. 8):
HMRC contends that if the appellant is to establish that he has a "reasonable excuse" for the late payment he must show that exceptional circumstances exist. That is not the test stipulated by the legislature. The words "reasonable excuse" are ordinary English words to be given their proper everyday meaning. There is no justification for the gloss that HMRC seeks to put on those words.
I notice that one of the Tribunal judges in that case has gone somewhat farther then before: In Ballysillan Community Forum v Revenue & Customs  UKFTT 257 (TC) the tribunal said (at para. 3):
I have to bear in mind that this is a case in which a penalty has been levied. In those circumstances the decision of the European Court of Human Rights in Jusilla v Finland (73053/01) ECtHR (Grand Chamber) is highly material. The Court decided that a penalty or supplement charged by the revenue authorities of a member country is in the nature of a criminal penalty and thus any proceedings in respect of it attract the provisions of article 6 ECHR (right to a fair trial). Thus, in my judgement, it is for HMRC to satisfy me to the criminal standard, so that I can be sure, that the required filing did not take place.
So, we have a two-pronged attack here on HMRC's insistence that an excuse must be exceptional: firstly, an ordinary reading of the enacting legislation (Schedule 55 of the Finance Act 2009) must be undertaken as the words "reasonable excuse" are not used with a specific definition. And since the European Court of Human Rights have held that a penalty to make a return is essentially criminal in nature, it requires a criminal level of proof.
I wouldn't be surprised if we see a first-stage tribunal determination based on one or the other of these points appealed. I personally am happy with the ruling based on the definition of "reasonable excuse" --- the phrase is clear, and I do not believe it to be ambiguous. Look, for example, at "reasonable doubt" --- a phrase that has been clearly understood in criminal cases for a very long time.
I'm not so sure though about the Jusilla point. It seems to me to be a fairly interpretive reading of the case. One point, though, does jump out at me: the Grand Chamber (at paras 32-34) concern themselves with the proportionality of the penalty. They have no problems with 10% (with a cap at some level), they do seem to have a problem with a fixed sum that is not in proportion to the tax owed.
It may be, ultimately, that "reasonable excuse" gets a legal redefinition, either judge-made or in statute, but fixed penalties get changed into percentage penalties. This may be of some advantage to the individual or small business: it may reduce the penalties on small errors. That seems fair to me.