past simple with 'moment ago'?

[mafto]

Hello. At first - I'm asking about British English; I know that the Americans use past simple more frequently.

I think we can use present perfect and also past simple in a sentence with 'a moment ago' with a change in the meaning.
Let us consider this conversation:

- Are you hungry?
- No, I've had lunch a moment ago.

I guess it is correct, expressing that the person's hunger is still satisfied by having eaten the lunch. That is why I think there cannot be 'No, I had lunch a moment ago' in the sentence. Am I right?
But I think there could be another conversation:

- Are you hungry?
- Yes, though I had lunch a moment ago.

Because in this case the effect of eating the lunch does not last by the time of speaking.
Am I right?

I'm asking this because I know that in BrEng, there is usually present perfect with 'just' but I do not know if 'a moment ago' is the same as 'just' with regard to use of tenses. I would say it is not.

So, to sum it up - I would like you to provide 3 answers (if the two conversations have to have only the particular tense or it could be changed (without changing the meaning) and if 'a moment ago' follows the same rule about associated tenses (i.e. present perfect) as 'just'.

Thank you very much :)
Have a nice day

[Bennevis]

In my humble opinion, "a moment ago" implies the past, and therefore requires the past indefinite tense. In other words, we should say either "I had lunch a moment ago" or "I've (already) had lunch". Please correct me if I'm wrong.

[5jj]

In my humble opinion, "a moment ago" implies the past, and therefore requires the past indefinite tense.

I agree - except that I call the tense the past simple.

[Tdol]

I would say I had lunch a moment ago- the present perfect sounds odd to me. (BrE speaker)

[Raymott]

I'd advise you not to use the present perfect with 'ago'.