What is the standard for citing granted patents and patent applications in a paper? For granted patents, three dates are available: filing, publication, and grant dates (see for example this patent). Which one should I use? The grant date seems to be missing from the original document itself. I would think that since the publication date is the date that is always present, it should be the date to use when citing granted patents or patent applications. However, the filing date is probably more important for the patent itself. So, which should I use?
There is no clear single standard. Personally, I would use the filing date, because this date is most important when establishing prior art (which might invalidate the patent, or parts of it).
Anyway, for unique identification the patent publication number (which is GB2468195 in your example) is more important.
When targeting a journal, you might want to check whether there is anything in their guidelines.