From this site,
http://www.ukpassportadvice.com/" Calls to 08719189073 are charged at standard BT National Rate at all times, calls from mobiles may cost more"
This site appears at first glance to be the official passport office with its title and Union Flag at the top
See my email to them below. No reply so far of course and as its a website we can't get the ASA to adjudicate until they change their rules.
Of course I suppose I should copy every one of these mails to Ofcom's board members.