Change of name and AN application!

Hi guys, I want to thank you all in advance for your time.
I have recently changed my name and I have deed poll certificate which I will include, I'm filling application with my new name but not sure to fill:

1.7 Name at the birth if different from above. ( If the name you have given are different or spelt differently from the name shown on your passport, please explain on page 15)
OR
1.8 If you are or have been known by any name or names apart from those mentioned above, please give details here.

My name on my passport is still old one.

I have filled 1.8 but I'm not sure if that is correct, can someone please help me and if is 1.7 correct, can I just cross 1.8 with a pen or do I have to fill a new application?

Many thanks guys.

I'm doing the same thing. I called the passport agency and asked them how I can get my British passport on my new name and they told me that I have to apply for Naturalisation with my new name so the certificate can be on my new name as well. After that the passport is easy. I hope this helps