Interests which may be legal or equitable may be registered as a result of the Land Charges Act 1925 (as amended by the 1972 Act).
The majority of interests in the Land Charges Act are equitable interests.
The idea behind Land Charges is to remove reliance on the doctrine of notice.
The doctrine of notice is a complex process but Land Charges supersede this.
If you have an interest which may registerable under the Land Charges such registration will constitute an actual notice to the potential purchaser of unregistered land.
If someone doesn't register a registerable interest under the Land Charges Act then that interest will be void at the point of purchase.
This will be the case even if the doctrine of notice is adhered to.