Thanks for your response.
I don't entirely understand your first suggestion; I tried googling it and then tried setting it to 'true', but this didn't seem to change anything.
I don't understand either how a hidden form field would help, since how would I know what it was called in order to see what value it had? The problem is that I don't know in advance the number of items that will be displayed, and therefore their primary keys/names.
Ideally I would like to be able to say 'give me the name of the button that was clicked' since that would tell me the primary key, but I can't say 'was it button x, was it button y' etc. since I don't know x, y, z in advance.
The only thing I can think of is that the primary keys are auto-increment integers, i.e. 1, 2, 3, 4...etc so I could keep checking if $form_1, $form_2, $form_3 etc. were set until I found it, but presumably it's not possible to dynamically change a variable $form_x to those values incrementally at run-time?
Thanks again, and sorry if/that I've missed the point completely.