Yes you can and you can do this at anytime after you have purchased your home. It is entirely up to you if you decide to staircase and purchase further shares.
You purchase additional shares at the current market value and with each staircasing transaction, your rent reduces according to the new percentage owned. When you reach 100% ownership, you no longer pay us rent, although you are still liable for service charges and ground rent (if applicable).
For more information about staircasing, click here