PAYPAL HTTPS issue

In OC 2.3x the notify_url sent to PAYPAL appears to be http://xxxx rather than https://xxxx.
This leads to an insecure data error from your browser as you go from PAYPALS https server to your incorrectly stated http: URL.

I have looked through the files and:
catalog/controller/extension/payment/pp_standard.php appears to have the line:
$data['notify_url'] = $this->url->link('extension/payment/pp_standard/callback', '', true);

In previous OC versions it was:
$data['notify_url'] = $this->url->link('extension/payment/pp_standard/callback', '', 'SSL');

Please can someone tell me how I get OC 2.3x to send a HTTPS notify_url rather than HTTP?

PS. I have set this in the PAYPAL Standard setting as HTTPS:// although I think this return address is ignored because OC sends it one.

Thanks!!!!!