What impact does a previous UK visa rejection have on future visa applications?

A previous visa rejection does not permanently affect your future applications, but it is always visible in your immigration history and will be reviewed by visa officers. The key impact depends on the reason for the rejection and how well you address it in your next application. For example, if the rejection was due to insufficient funds, or improper documentation, you will need to clearly fix those problems in your new application with sufficient funds and/or proper documentation.