Idealy you should record the ethnic background of all aplicants, not just the ones that you take on.

One day - a bloody time wasting do-gooder from the council will turn up and demand to know what percentage of your applicants come from which ethnic group and what percentage of them you employed.
It happened to us!
Demanded to know why we had only interviewed one candidate from an ethnic minority..... Only one applied!
And we gave him the job - so thats 100% , so sod off!

We also ask if they are legally allowed to work in the UK and would they be able to provide evidence of this.

Good Luck!