It is good practice to keep a log - a record of the navigational activities on board. Information in the log can then be used to establish the vessel's position in the event of an electronics failure or for investigations following an incident.
In accordance with the Merchant Shipping (Safety of Navigation) Regulations 2002, which require compliance with Chapter V of the annex to the International Convention for the Safety of Life at Sea, all UK vessels on international voyages (other than pleasure vessels of less than 150 gt) must keep on board a record of navigational activities such that it is possible to reconstruct the vessel's track throughout the voyage.
Primarily, the record should be made in the vessel's log book. If any other form of navigational aid is used (such as electronic or paper charts) then these may be erased at the end of the voyage (although they must be retained if there is an incident during the voyage), provided that the information is also recorded elsewhere, for example in the log book. Position recordings should be made at regular intervals, sufficient to enable the voyage to be reconstructed.
There are no specific requirements for pleasure vessels of less than 150 gt, although the RYA encourages all pleasure vessels, whatever their size, to maintain a detailed log book as a matter of good practice. All vessels that proceed to sea (including pleasure vessels) must have in place an adequate passage plan - the level of detail necessary will depend on the size of the vessel, its crew and the length of the voyage.
Enforcement of this legislation in the UK would normally be by the Maritime & Coastguard Agency - in terms of navigation and passage planning, any enforcement would normally take place after an incident that the MCA was called to investigate.