Fail grade for Edexcel = N or U?

I thought it was U, ungraded, for all exam boards

I understood it as both are applicable but in different circumstances. U means you didn't reach the minimum grade level so you failed, N means it's 'not markable' because you didn't do the correct tasks. E.g. if you started solving quadratics in an english exam you'd get an N (presuming you did no coursework as well of course).

No U is to an insufficient standard. So in an english exam if you got a question like: 'How does this character feel?' a U student would write something like 'he is sad' and an N student would write 'y=x³'

Or at least that's how I understood it, I'm probably wrong.

i didnt know that an N existed!

As far as i was aware, you can only get grades A, B, C, D, E or U

Grades and grading history
Originally, A-levels only distinguished between a pass and a fail, although fails were divided into two types: one meaning that the student had failed a subject at A-level but passed at the O-level equivalent of that subject, and the other meaning that the student had not passed at either A-level or O-level. In 1953, another grade was introduced: the distinction, for high passes. Due to complaints from universities that the grading system was not specific enough to identify the students they wanted, a grading scale close to the current one was created in 1963, which retained an O-level pass between the grades E and F (Fail).[3] They also introduced norm-referenced grading, which meant that only a certain proportion of candidates will achieve certain grades – 10 % A, 15 % B, 10 % C, 15 % D, 20 % E and a further 20 % allowed an O level pass.[6] In 1984, the Secondary Examinations Council advised that grade boundaries should be based on the partition of the mark scale rather than on proportions of candidates, in a move towards a criterion-referenced system. Examiner judgement was to be the basis for the award of grades B and E, with the remaining grades determined by dividing the mark range between these two points into equal intervals. This system was introduced in 1987 and remained in force until the introduction of the new curriculum in 2000.[7] When GCSEs were introduced, and also to resolve the long standing problem of the narrow spread of marks between the grade boundaries, the O-level pass was dropped, replaced by a grade N, standing for 'Near miss', which was a much narrower denotation for candidates who failed to achieve the minimum standard for an A-level pass by only a few marks. The grade F was also replaced by a grade U. With the increase in the modular structure of the A-level examinations, the retention of the grade N was considered unnecessary as there was far more information to indicate how close a candidate was towards achieving a pass based on the modules taken. Therefore, with the introduction of the new revised A-levels in 2001 under Curriculum 2000, the grade N was finally dropped.

In the current system, A-levels are graded from A to E, along with a fail grade, U (Unclassified or Ungraded).[8] The raw mark in papers are converted to Uniform Mark Schemes, so that every A-level is out of 600 UMSs, and every AS-level is out of 300. Percentages of these UMS scores are: 80% is an A grade, 70% is a B grade, 60% is a C grade, 50% is a D grade and 40% is a E grade; anything lower is unclassified (U).[8]

See bold. Hope this clears it up.