Under the provisions of FA03/SCH17A/PARA18A, where a tenant makes a loan or pays a deposit (whether to the landlord or to a third party) the repayment of which is contingent on anything to be done or not to be done by the tenant:-
The same provisions apply to loans made or deposits paid by an
assignee in connection with the assignment of a lease. In this case
the relevant maximum rent is the highest rent payable in respect of
any continuous 12 month period during the first five years of the
term remaining outstanding as at the assignment date.
For details of how SDLT is calculated on such arrangements, refer to SDLTM13040.