I don't think your status is a problem for the moment, but if your passport really has gone missing in the post you need to sort out the problem immediately. What do you mean by recorded proof of the postage? There are three options in the UK which are proof of posting (free), recorded signed for (cheap), or special delivery (expensive) - which did you use? Though to be honest it is not advisable to use anything but special delivery when posting passports/visa applications.