Rent Review Clause

General Discussion

I acquired a property with a tenant in-situ so I inherited the tenancy agreement from the previous landlord. It includes a rent review clause which states the following; 

"It is agreed that the rent as defined in this Agreement will be reviewed on the anniversary of this Tenancy and upon each subsequent anniversary in line with the change in the Retail Prices Index (RPI) for the previous 12 months and the rent varied accordingly either by way of an upward or downward adjustment."

I would like to increase the rent on the next anniversary which will be on 25 March. My question is the RPI figures for March are not published until end of April. In order to set the new rent for March 25th and to give the tenant a months notice I would have to use the figures for December or possibly January, depending on what date in January they are published. Is that the correct procedure....

Many thanks