Naturalisation Application: Father's Surname & Previous Visa

Dear Members,

I am in the process of filling up the application for Naturalisation and I have following two queries;

1] I am asked about my father's surname in the application. He doesn't have a surname and in his passport the surname field is empty but the application form doesn't let me leave the surname field empty.

2] Also I am being asked about the previous Visa I had. The exact question is within quotes.

"Do you have a previous visa, entry clearance or leave to remain where you had to prove your knowledge of English?

Tell us the previous visa, entry clearance or leave to remain you had"

Before applying for ILR I was on Tier 2 General. In that case, I believe, I shall put Tier 2 General?

Could anyone please advise regarding above two queries?

Many thanks.

Regards
Shahab

1] I am asked about my father's surname in the application. He doesn't have a surname and in his passport the surname field is empty but the application form doesn't let me leave the surname field empty.

put 'nil'

Before applying for ILR I was on Tier 2 General. In that case, I believe, I shall put Tier 2 General?

Yes