E67 - interesting that you NOW bring up Lasors as an answer (and a different one at that) to your original question and answer.
The time to do this sort of study is BEFORE the first attempt at the flight test.
In answer to your question: Half the guys at the CAA will constantly tell you that "the answer is in Lasors" - the other half will constantly tell you that "Lasors is riddled with errors and, as it is not the source document, is effectively worthless" (Yes - annoys the hell out of me, too).
The "source document" is the JAR-FCL. Nothing else.
As I said before - the original CAA approval for public transport flight was based on factors of 1.33 to go - and 1.43 to come back. JAA said 1.25 - so any UK operator using the JAA figure of 1.25 was breaking UK law, as it gave reduced runway lengths for public transport operations.
The CAA, in their efforts to adopt international standards, then gave all operators a "letter of exemption from the law" to allow them to operate to the new (lower) figures.
Flying schools were invited to choose which figure to use - and specify it in their manual. That is the figure that must be used whilst operating at that school.
Please feel free to ignore the advice that you have asked for and use your own figures. Just hope that your commercial examiner doesn't read Pprune (some of them do) and, as such, isn't aware that having been given the answer, you don't have the intelligence, sense or interest to approach your second attempt at the test with the correct information (even when you now know where to get it from).
Publications do NOT get updated at the same rate (if ever) as the material that they discuss - I've just found out, through an informal conversation with a friend at the CAA, that insurance is now mandatory for the operation of a UK registered aircraft. It doesn't say that in the text books - at least not at PPL level air law.