Here is a little bit of information:
During this 15-day notice period any person can register a "caveat" using forms obtained from the register office, giving a legal reason why the wedding cannot proceed.
http://news.bbc.co.uk/1/hi/uk/4328557.stm
This is why a notice of an intended wedding must be displayed to the public for 15 days before the wedding, and why any wedding venue must have public access - so objections can be made during the ceremony.
http://www.grantrileyweddings.co.uk/pages/faq. html#Anchor-What-37516