You can use your P2P or ISA balance to make an investment by choosing the peer to peer investment you would like. You click invest now and on the next screen you will be asked to select "Which account would you like to hold this investment in?' You can select 'My IFISA Account' or 'My P2P account'. Please note you will need to have an available balance to cover the full investment amount, OR you can 'Add funds' from this page.