I think you don't get it - a person can have ILR for 10 years it doesn't matter, but for naturalisation it will only be the 5 or 3 years before date of application that are taken into account for residential requirements.
You can apply for naturalisation on the basis of 5 years or 3 years as it is based on 5 or 3 years before date of application.
The UKBA website has all the information and your friend will need to meet all the standard requirements.
http://www.ukba.homeoffice.gov.uk/briti ... uirements/
Residential requirements - 5 years
To demonstrate the residential requirements for naturalisation, you must have:
* been resident in the UK for at least five years (this is known as the residential qualifying period); and
* been present in the UK five years before the date of your application; and
* not spent more than 450 days outside the UK during the five-year period; and
* not spent more than 90 days outside the UK in the last 12 months of the five-year period; and
* not been in breach of the Immigration Rules at any stage during the five-year period.
Residential requirements - 3 years
In order to demonstrate the residential requirements for naturalisation you need to:
* have been resident in the United Kingdom for at least three years (this is known as the residential qualifying period); and
* have been present in the United Kingdom three years before the date of your application; and
* have not spent more than 270 days outside the United Kingdom during the three-year period; and
* have not spend more than 90 days outside the United Kingdom in the last 12 months of the three-year period; and
* have not been in breach of the immigration rules at any stage during the three-year period.
When does the residential qualifying period start?
The residential qualifying period is calculated from the day when we receive your application. Most unsuccessful applications fail because the applicant was not present in the UK at the beginning of the residential qualifying period. You must make sure you meet this requirement before you make your application. For example, if we receive your application on 25 March 2010, you must show that you were in the UK on 26 March 2005.