Add unique invoice/order number to CGBetterForms

[pwg]

Hi, a client wants me to develop a landing page and form, which when submitted will send back an auto-generated quote. Fairly basic parameters.
One thing I am stuck on, is how to add a unique invoice or quote # to each reply email (quote)?

I tried {counter} but this seems to reset each page load, and am now using a formatted date output {$smarty.now|date_format:'%Y%m%d%H%M%S'}, which is ok, but not ideal.

Any suggestions?

As an aside, CGBetterForms is excellent. Many thanks!

Any help appreciated,

Cheers,

Paul