The rules vary uni by uni. So pick a uni you're interested in applying to, and search for their contextual offers page.
Factors which are aften used are your (or your school's) postcode - to establish whether you're in an area where not many people go to uni, whether you're eligible for free school meals - as that's an indicator of low income, whether you've ever been in care, whether you're the first in your family to attend uni, etc. etc.
As I say, the rules can vary a lot (and can also get quite complicated in some cases), so you need to check each target uni one by one. Many have on-line tools where they'll ask you a few questions and give you an indication of whether or not you're likely to be eligible for a contextual offer.