Read only access for Guests

Make sure that the Permissions are set for guest also. In your case, you probably want List/View selected.
Al

Thanks for your message - I do have Guest permission set to List/View already. As mentioned Guests can view the list when either of the other two Advanced Security Settings options are used. It is only when selecting "Users can see and edit their own data only" that a problem arises.
Brian

I'm not sure if you can do this with guests because there is no link to the main table. Normally this would be based on a field (ie. like a username). You might have to wait for Admin to answer this one.

As I have had no further responses to my query, I have been doing a bit of experimenting!
I have discovered that there is the ability for guests to have read only access when using the setting "Users can see and edit their own data only". However this appears to be the case only if the menu page has two or more tables listed. If I then use the menu builder and delete all but one table then I am directed to a blank menu.php page.
This does not appear to be the case if I then change the Advanced Security Setting to either of the two other options.
As background there is an existing genealogical database of Surnames which has been contributed by over 4,000 users. Currently the data is sent to a volunteer administrator who places it on a web page. What I am seeking to achieve is the ability for anyone to look at the Surname data but to allow the contributor to manage their own additions, deletions and edits. By necessity it needs to be simple so I don't want the contributor to have to trawl through every entry to find their own data. The setting to see and edit their own data only is ideal for my purpose. At the same time I want the availability of the data to be read only to be also easily available. I just can't seem to crack this final obstacle!

BrianL,
this explanation makes total sense.
I would recommend to separate views for guests and for authors. I.e. you can create a custom view for this table (Datasource tables screen) and setup different access rights. Allow guests to to access this custom view only (via User Group Permissions) and do not set Advanced Security options on this view.
Authors, in turn, will be able to access main table where you can set 'Users can see and edit their own data only' mode.
Hope this makes sense.

Sergey
Thank you for pointing me in the direction of Custom Views - I had wondered whether this might be an answer and it does meet most of my requirements as guests go directly to the data and can view without problem.
However the users (authors) are taken to a menu and have to decide which table they wish to view whereas I would like them to bypass this and just go straight to their own data. I have again tried to achieve this by deleting the custom view from the menu builder leaving only the original view in the menu and this brings up the blank menu.php page as before. It appears that there is no way of skipping past the menu.php page when there is only a single page being referenced. Or have I misunderstood?
Brian

Brian,
you can add AfterSuccessfulLogin event to redirect users to that table with their own data.

Thank you Sergey - it now works as required.
I think that my brain had given up as your solution was so simple! The only additional thing to do was to amend the html in Visual Editor for the Login Page to redirect the login for guests to the new custom view page.
Brian