For any guarantee to be valid, it needs to be in writing and it must be signed by the guarantor (Statute of Frauds 1677).

Section 6 Law of Distress Amendment Act 1908 enables L to serve a notice on a sub-T, when T is in arrears. The effect of serving the notice on the sub-T is to assign T’s right to receive the rents from sub-T over to L. Thus, once a notice is served on the sub-T, the sub-T then becomes the immediate T of L (and sums payable under the notice are deemed to be the rent).

Many leases contain a provision saying the rent in any sub-lease must be the greater of the open-market rent, or the passing rent under the existing lease.