Unlike other countries there is no such thing as a green card for UK. There are a number of immigrant visas available. You can apply for a green card through online from http://www.visa4uk.fco.gov.uk/.
Guidance on every type of UK visa is available here http://www.ukvisas.gov.uk/en/howtoapply/… and all the information on points-based visas is down the bottom of the page.
Following are the requirements to get a UK citizenship:
- The person should stay for at least 5 years before the date of your application (unless your spouse or civil partner is a British citizen)
- Should not spent more than 450 days outside the UK during those 5 years
- Should not spent more than 90 days outside the UK in the last 12 months
- Been granted indefinite leave to stay in the UK
- Had indefinite leave to stay in the UK for the last 12 months
- Not broken any immigration laws while in the UK