How honest should I be?

I left one group after someone came in who talked over me and dominated every conversation with topics others had little grasp of and couldn't join in. Also when we went out she decided we would all split the bill even though some had no drinks or pudding.

I don't think it is helpful to ignore mentioning the real reasons you don't want to continue. Unless you make your reasons for resigning very clear and say why you feel as you do, nothing will ever get any better.

I had this recently when I notified the chairman of the choir I was in, exactly why I was going to leave. Basically a new conductor changed the whole style of the choir from a good Choral Society into a very chaotic choir with little planning and little attention to detail.

This was not the what we had been paying our subs for.

I was as diplomatic as possible but if I had not explained why I was really dissatisfied no one would actually try to put things right. (I am still not sure if it will improve until it has first got worse, but it needed saying)

A lot of other people have crept away from this sinking ship to other better societies.

I've recently resigned from two groups.
One because, like you say Morgana, the Chair thinks he is still at work, orders us around, vetoes anything that is not to his taste and generally makes it clear that he doesn't rate anything done by a woman. This is why the Committee is five members short! But I just said I had other commitments because he has such a firm grip nothing will change.

In the other case the organisation is simply going in a direction that I am not comfortable with, though this doesn't mean it's the wrong direction. Just that I can't lend it my support. I was honest in my resignation there.

I'd give the same reason to both groups, making time for other pursuits sounds reasonable enough. That way you are consistent and avoid awkwardness if you bump into anyone.

I’ve just told a voluntary organisation I would like 6 months time out of volunteering due to other commitments. No more specific than that. That way I will remain ‘on the books’ and can go back if I decide to give it another go. The positive response made me wonder if they are as fed up with me as I am with them .

No, I agree that it is difficult. In principle, the group should know. In practice, what difference will it make? I think Teetime is right - sometimes groups run their course.
Also, without knowing the nature of the groups and their aims, it may just be that they need to change, and you need to go elsewhere!
I would definitely leave the first group you mentioned. It may be that you then find yourself feeling differently about the second one. If not, give yourself a cut off date.

Thank you for all your comments. The problem with both groups is largely to do with new people who have joined and either disrupted or changed the whole ethos of the thing. Largely, its the men empire building - think they still consider themselves to be at work!!!

I would like to be able to give feedback on why I am leaving - in a constructive manner - but not sure whether I can do this, especially as I shall still be seeing people from both groups. One group (a Committee) I am going to say that after ten years, I would like more time to pursue other pursuits - it is a very time consuming responsibility. The other group is more problematic and I haven't quite decided what to do - its leader is going through troubled times at the moment, but I really don't want to keep attending it. I would prefer to be honest, but that is not always possible, is it?!!

It depends on the group and the reason. I have just stopped volunteering with a charity because they have a very complex and user unfriendly computer system and provided no support for new users. I enjoyed the work and did it well.

I made it very clear why I was resigning, although they didn't need telling and were very offhand about my departure.

I think some of these groups like some relationships have run their course whatever the main reason for wanting to stop is. i would be inclined to just say that - I think we have gone as far as we can together - or in an ironic tone - it's not you it's me.

It depends on so many things:
are you likely to want to resume?
would your reason be helpful to the group - either to know they are doing something wrong; or to know that they are OK but no longer your cup of tea?
would the reason be hurtful without be helpful?

I would imagine yourself bumping into one of the group in a year or so's time and them asking how you are. Would you be happy to see them and chat, or would you feel embarrassed? That's often, though not always, a good way to gauge the best thing to say.

It would depend what the real reason for leaving was Morgana. .

If it is because you (or someone you care about) is ill, then tell them the truth.
If its because you have other more pressing things to do, then tell the truth.

If its because you can't stand the sight of someone, maybe you should be a bit more economical.

Couldn't you just say "personal reasons" to both groups? If they push you, you can just say you don't wish to go into it further.

If it will be hurtful why do it? If constructive and positive go ahead.
If, however you mean do you have to give reasons of a personal nature then no, a general "sorry but I can't manage to fit this in any more" is enough.

Of course am fascinated to know why you are giving up. Please let us know. It helps to know why people leave. But I think you need to be diplomatic.