The draft regulations enabling the Financial Conduct Authority to regulated peer-to-peer lending have been published for parliamentary approval (see Articles 36H-I). There have been some changes to since the previous version in the March consultation to remove certain issues. The more detailed FCA rules should be out with a further consultation paper in September/October.
Basically, your platform is 'in scope' for FCA purposes if it enables loans to which individuals are a party as lenders and/or borrowers (either on their own or as a member of an unincorporated association or a partnerships of two or three). However, there is an exception in the case of borrowers, where either the lender provides the borrower with credit of more than £25,000 or the loan is entered into by the borrower wholly or predominantly for the purposes of a business carried on, or intended to be carried on, by the borrower.