(1) If it is your primary access, ie your only access, then nobody can stop you from using it. It should not be all that difficult to establish your right, but you will have to start with the Land Registry and it may have to go to Court for an Order enabling the LR to act
(2) If it is a secondary access it may be more difficult.
(3) It does not matter at all who owns the land, so waste no time over that
(4) The LR offers a full search regarding Rights of Way. See
http://www.landsearch.net/boundaries.asp and scroll down to BND 3
(5) There is no such thing as a "public right of way on foot". Please explain.
(6) The previous owner document to which you refer is presumably a Statutory Declaration.
(7) What you are seeking is a statement on your Register at the Land Registry that you can "pass and repass on foot and by vehicle at any time by day and by night" over the land.
(8) Check whether the land is Registered by going to
http://www.landreg.gov.uk/ (you need the Title No as a reference). If it is not, contact your local District Land Registry Office and ask them to issue a Title Number (it is not necessary for you to Register the land).
(9) If it is the primary access your property is blighted and will not sell until you now establish at the Land Registry a right to access that cannot be disputed
(10) whilst there is a minimum period for a prescriptive right a lesser period will be just as acceptable if it is your primary access