<p>I'm trying to get a specific asp:button onclick event to fire when I press the enter key in a specific asp:textbox control.</p>

<p>The other factor to be taken into account is that the button is within a asp:Login control template.</p>

<p>I've no idea how to do this, suggestions on a postcard please.</p>

You need to do it with javascript. It's really easy with
jQuery.
You can do something like (off the top of my head, not tested):
```
```
$('#myTextBox').keypress(function(e){
    if(e.which == 13)
        $('#myBtn').click();
});
```
```
Edit: Be aware that although jQuery works exceptionally cross browser, there are some quirks with keypress described
here
.
Whoops i didnt see you said the "enter key" i thought you said "any key", yeah in that case use DefaultButton on asp:panel