Am I obligated to declare my STEP result on UCAS?

I don't think you have to declare it.

You must declare all examination entries and results on your UCAS application, or else it can be cancelled by UCAS.

So how much would I be disadvantaged if I declare the result on UCAS, and how can I provide Proof of my result, as STEP as a entrance exam do not have certificate.

So how much would I be disadvantaged if I declare the result on UCAS, and how can I provide Proof of my result, as STEP as a entrance exam do not have certificate.

STEP results should be sent by the exam provider to the university directly via UCAS, so you shouldn't need to list it on UCAS. It is an entrance test, and these are usually sent by UCAS only to universities who require the result of the test (e.g Cambridge for mathematics). The same would apply for a UKCAT (UCAT) score for example.

II took them in year 12, without holding any offer, so they weren't sent to any university.

Well that was a bit of a pointless exercise wasn't it? As you probably realise now, STEP draws material from the full A-level curriculum, including material normally covered in year 13. Hopefully this experience has taught you that taking exams you are not prepared for is at best a meaningless endeavour and at worst could backfire.

That aside, they may or may not send the results for the previous sitting. If they do, and you haven't declared it, the university could well consider that a form of academic misconduct, which would be reason enough to reject you. If they don't send them, and you have declared it, they will probably focus on the current year's sitting as that would be indicative of your current ability, which is what they are looking to assess.

You should assume your previous sittings will be sent along with your current one, and the universities will see it anyway. In which case it would be much better to have already declared it, than to appear as though you are trying to deceive them.

If you're applying to a course that requires STEP, you will presumably be taking STEP again this year, and you will receive a conditional offer which you will achieve the STEP condition in this year's sitting. If you aren't applying to a course that requires STEP, it's irrelevant anyway.

Either way, it doesn't make a difference.

I know. But the problem for me is that I took them in year 12, without holding any offer, so they weren't sent to any university. I just took them to challenge myself, before I summit my UCAS application. I am just hoping in year 13 I won't force to summit the result I got in year 12.

That is fine, you do not need to declare it on UCAS because it is an entrance exam; it is only sent at the point of application to universities you apply to that need it. You presumably have the PDF certificate for it, so keep that as proof that you sat it already. If I were you, I would contact the exam provider and ask them how long the result is valid for, and for which application cycle (e.g 2019 entry or 2020 entry). If the STEP result you got will be invalid for the cycle you will be applying (I assume this is for 2020 entry), it shouldn't be a problem, as you would need to sit the STEP again anyway, and the new result would supersede the original one. You might still need to declare it, but you would need to contact universities individually to know this. Entrance test exams don't usually last for longer than one year in any case, so don't stress about it and find out if the old test result will be valid for 2020 entry or not.

I hope this helps. You must always list qualifications on UCAS, but the STEP exam is a separate issue.

You must declare all examination entries and results on your UCAS application, or else it can be cancelled by UCAS.

UCAS say (https://www.ucas.com/about-us/policies/privacy-policies-and-declarations/ucas-undergraduate-declaration):

"If we, or a university or college, have any reason to believe that you or your referee have:

left out any relevant information, including qualifications you have completed, qualifications with an unsuccessful grade or qualifications for which you are still awaiting results"

STEP is an admissions test, not a qualification (there is no certificate for it), and therefore doesn't need to be declared, just as you wouldn't need to declare that you previously took, e.g. the Oxford MAT.

I am applying economics for Cambridge. Also applying mathematics and economics for Edinburgh,ucl, lse and warwick( STEP for (UCL and warwick for an alternative offer). I am just worried if I declare the result on UCAS, they would reject me for getting bad STEP grade, as all the course I apply related to math. But anyway, if I am forced to declare it, I would.

There is nothing implying that is an exhaustive list of "relevant information". The phrase "relevant information" is the key part of that statement, not "qualification". Universities may well deem it "relevant" whether an applicant took STEP previously or not (particularly if the OP is applying to courses which do require them to sit STEP in the year of application anyway).

I mean, they did explicitly use the word 'qualifications' three times... by this argument, surely things such as mock exam grades, in-class test marks, maths challenge certificates, whether you're a re-applicant etc. are also 'relevant', yet no-one's suggesting that these should be declared on UCAS by default.

The difference is none of those are public examinations which are externally marked and moderated, which STEP is.

The result is valid until 31 January 2020. Should I declare it in this case?