My step-father recently tried to buy £500 of premium bonds. His application was returned because he was not on the electoral register (he has just moved house).
National Savings asked him to provide various documents to prove his identity, including a photocopy of his passport. This had to be "certified" by one of a limited group of people: " a professional person such as a banker, authorised financial intermediary, mortgage broker regulated by the FSA, teacher, doctor, minister of religion or civil servant."
This seems disproportionate in order to buy a few premium bonds. Moreover, the range of people who can "certify" the copy of his passport is much narrower than the range of people who can validate a passport application (www.passport.gov.uk/passport_countersign.asp)
Any crook could easily forge the "certification". All the requirement does is to cause hassle for law-abiding people.