252. Form of sub-mortgage.

Where the principal mortgage is a legal mortgage of land1 by demise or sub-demise2, a legal sub-mortgage may be effected either by sub-demise for a term that is at least one day shorter than the principal mortgage term or by a charge by deed expressed to be by way of legal mortgage3. A sub-mortgage which purports to be by way of assignment of the principal mortgage term takes effect by way of sub-demise but is subject to cesser on redemption4