HMRC uses case law as authority for spreading additions into earlier years and its officers are encouraged to follow the guidance in its enquiry manuals at EM3309, which states:
"If you have proven omissions for which there is no ready explanation and the business and way of life of the taxpayer have not changed you will be in a much stronger position to argue for addition to other years.
Taken together, then, the tax cases EM3310+ demonstrate that, in the absence of evidence to the contrary, a `presumption of continuity' can be made and the Inspector can be entitled to conclude that under-declarations in some years can be taken as a pointer to under-declaration in others and make discovery assessments accordingly."
The tax cases referred to are:
- Jonas v Bamford [1973]
- Rosette Franks [King Street] Ltd v Dick [1955]
- Nicholson v Morris [1977]
- Bi-Flex Caribbean Ltd v The Board of the Inland Revenue [1990]
Probably the most well-known of these cases is Jonas v Bamford, in which the judge expressed the presumption of continuity as follows:
"Once the inspector comes to the conclusion that, on the facts which he has discovered Mr Jonas has additional income beyond that which he has so far declared to the inspector, then the usual presumption of continuity will apply. The situation will be presumed to go on until there is some change in the situation, the onus of proof of which is clearly on the taxpayer."
However, the recent case of Barkham v Revenue and Customs [2012] now suggests that the presumption of continuity may not apply as liberally as HMRC might wish.