I filled my tourist visa applications online and was able to save them and return to them with no problems. You must take a note of the reference no your quoted at the start of the application.
we do not use ID cards in the UK so you would leave that blank.
I assume your using the link as below to start your application?
http://in.vfsglobal.c...nlineapplication.html
There are other websites posing to do your visa for you but vfs.global are the only ones accepted by Indian Embassy.
References are just people who have known you for some time. Just to make sure you are a bona fide applicant. I supplied references but they were never contacted.
Had to save my application a couple of times, to find out answers!!!
If it's a tourist visa enjoy your stay ☺