This visa form falls under the UK settlement route
If you have lived in the UK for 10 years and you have held valid visas during that period, not left the UK and obtained a new entry visa or held any type of visitor visa during that period, you could be eligible to apply under this settlement route
If part of your 10 years in the UK was under the EEA regulations, this does count towards your 10 years even if some or majority of your UK stay was under immigration control
The key to the success of this application type is your 10 year visas for the UK, travels made out of the UK in this time, no criminal convictions
If you hold a tier 2 visa, you do not need to meet the £35500+ income level or require the tier 2 sponsor to provide you a letter confirming continuous employment
This visa route is very popular where the person first entered the UK under student visa, then switched into Tier 1 Post Study Work visa, then switched into Tier 2 General
Another popular journey for this visa route is Study visa, switching into Tier 2 visa, then switching into family partner visa route