Does anyone know anything about passports...?

[SpunBodgeSquarepants]

I need to get a passport for DS who will be 5 in two weeks. His father and I are seperated - he is on DS birth certificate and was registered with his surname. However around 2 years ago we changed DS surname to my surname via deed poll.

Will it be straightforward to get him a passport with his new name? Obviously I will send off the passport form with his birth certificate AND deed poll certificate.

I can't see why it would be a problem. It's not a problem for name changes due to marriage. If you do the application online it tells you exactly what you need to send along with photos and declaration.

That's very true.

Does anyone know whether I need permission from his dad to get him a passport??

You don't need permission from his dad.
I'm zero contact with xp and had no problem with the dc's passports. I did include their dads name and date of birth on the form though.