Some time ago now, I wrote about an interesting set of questions which had been referred to the Enlarged Board of Appeal, the EPO's highest appellate body.  These concerned a thorny problem known variously as "toxic divisionals", "poisonous priorities", "self-collision" and so on.

The full details of the background to these questions are in my earlier blogpost.  To recap briefly, imagine a situation where a first patent application discloses subject matter "A" (imagine "A" is "copper", for example).  A second patent application is then filed, claiming priority from the first, but although it retains the disclosure of "A", it contains a claim to "B", which encompasses "A" but is broader (imagine "B" is "metal", for instance).  Now imagine that the first application (or a divisional of the second application) is published.  Is the claim to "B" entitled to the earlier priority date?  If not, does the disclosure of "A" in the priority application anticipate the broader claim to "B", depriving it of novelty?

Different Examining Divisions and Boards of Appeal had taken different stances on this matter.  Some of them had ruled that the later claim to "B" was not entitled to an earlier priority date, and so the disclosure of "A" was indeed a novelty-destroying disclosure.  Others had ruled that the claim to "B" was entitled to priority to the extent that it covered "A", so there was no novelty problem.  This divergence in practice led to a number of questions being referred to the Enlarged Board of Appeal to resolve.

The Enlarged Board has now released an order stating the following conclusion:

Under the EPC, entitlement to partial priority may not be refused for a claim encompassing alternative subject-matter by virtue of one or more generic expressions or otherwise (generic "OR"-claim) provided that said alternative subject-matter has been disclosed for the first time, directly, or at least implicitly, unambiguously and in an enabling manner in the priority document. No other substantive conditions or limitations apply in this respect. 

That wording is confusingly opaque, but in simple terms it seems to mean that the "poisonous priority" or "toxic divisional" concept is gone for good.The full reasoning has yet to be published, but based on the nature of the questions referred and the submissions on file, I expect that the Board will adopt the so-called "Tufty's Law" approach (named after the blogger "Tufty the Cat", who was one of the first to draw this issue to wider attention). Essentially, in this approach, the claim to "B" can be mentally divided into:

a portion that claims "A", which is entitled to the earlier priority date, and so the publication of the priority application or divisional disclosing "A" cannot be considered prior art against this part of the claim;

and

a portion that claims "B minus A", which is not entitled to the earlier priority date.  The publication of the priority application or divisional disclosing "A" is prior art against this portion of the claim, but it does not pose a problem for novelty because there is no disclosure of "B minus A".

This approach had been adopted in a number of Technical Board of Appeal decisions prior to the referral, such as T 1222/11, and it seems likely that the Enlarged Board will confirm in its written decision that this is the correct approach.For patent owners and their patent attorneys alike, this decision should come as welcome news, as - despite the complicated concepts involved - it brings some much-needed clarity to an area of European patent practice which had given many of us headaches over the last few years!