Ah, a 'Benefit' of electronic Land Registry and loss of paper records. A footway box won't be recorded in the deeds but covered by a separate 'Wayleave' document that would have been included with the paper deeds (records). Quite possibly a member of the solicitors staff who dealt with the house purchase didn't recognise the significance of the document.
If the footway box has a Wayleave associated there will a payment made for it being on your land, as with most payments that is most likely an electronic transfer paid once every few years (3,5 or10); quite possibly still being paid to the original property owner.