Just happened across this whilst browsing some info on ownership of watercourses, thought it might be of interest since boundary issues seem to feature quite frequently. Only a short read and some useful 'legal presumptions' in section 11.
HM Land Registry plans: boundaries (practice guide 40, supplement 3)
HM Land Registry plans: boundaries (practice guide 40, supplement 3) - GOV.UK
WWW.GOV.UK