You could get a map of the property, do a mapping search in the land reg to see if registered or unregistered. If unregistered really best thing to do is go to a solicitor. If registered get a copy of the folio- it will show whether an original title deed has issued or not. If it has issued then this is presumably what they lost, although its worth checking that it really was released to them by the bank and not a copy. Again probably best at this point to contact a solicitor who can apply for a new land cert- takes affidavits, advert etc. They could short circuit the whole thing and go and make an appointment with a solicitor who has an on line account with the land registry who can make the searches there and then while they are with her/him- the cost will be very little just to check out the situation. Bear in mind that people often come in to me with what they think are their original title deeds and they are nothing of the kind. So your parents might have nothing to worry about.