English Heritage has recently published the new Guidance for Divers, ‘Accessing England’s Protected Wreck Sites’ document. See http://www.english-heritage.org.uk/publications/guidance-for-divers/ This fully explains how to apply for a licence for a designated site (including those wishing to apply for a visitor licence).
The Department for Culture, Media and Sport has also just published the Advisory Committee on Historic Wreck Sites Annual Report 2009 for the UK. This includes details of the sites designated under the Protection of Wrecks Act 1973, as well as a list of current licensees. It also includes a map of the military wreck sites in UK waters designated under the Protection of Military Remains Act, 1986. This act allows the Ministry of Defence to protect the remains of aircraft and designated vessels that were in military service when lost from unauthorised interference.