How to change my DS's surname?

[Francescal88]

Ok so a bit of background - DSs dad and I got together in December 2012, fell pregnant in June 2013 (very much unplanned) and DS was born February 2014. His father and I have never lived together (my DS and I are still living with my parents at the moment).
So DSs father and I had been pretty on/off since September until we decided to call it a day before Christmas. Apart from £50 the month after baby was born, I have not had a penny of help from him which was very very tough whilst I was on SMP. I went back to work part time in November but unfortunately I've had to now hand in my notice as I cannot commit to going back full time. Things are going to be even tougher for DS and myself. I opened a case with CMS in November and my lovely ex partner was supposed to start paying me £194 at the end of January. I, of course, am yet to receive anything.
But anyway, I digress. I really, REALLY do not want my son to be known by my ex partner's surname (as is on his birth certificate) anymore. I made the decision to put my ex's surname on my son's birth certificate as at the time I was happy, and thought it would save me having to change his name after we got married. But in the past year my darling ex has been pissing most of his wage on cocaine and I stupidly dos not realise until DS was about 6 months old. There was always some excuse, some reason why he couldn't help me out financially that month.
I know the easiest way is for my ex just to sign a document giving permission. But he's refusing. Is there another way? How much trouble would I be in for forging his signature?

Forgery is a crime. Please please please do not become a criminal. I do not know if you have legal recourse but your dc to be known by his fathers surname is not worth going to prison for.

In most circumstances it isn't possible to change the name on a birth certificate and you can only apply to change who the father is if a DNA test proves (or a court order says) that the man named on the certificate isn’t the natural father.

There is no legal procedure which must be followed in order to change the name a child is known by, providing all the people who need to give their consent have done so. Where only one person has Parental Responsibility for a child, that person can lawfully change the child’s name. Where two or more people have Parental Responsibility for the child, one of them can lawfully change the child’s name if all the others agree. So as the father is named on the birth certificate he has Parental Responsibility and you need his agreement to change the name or permission from the court.

I thought this was the cause. Thank you for your detailed answer though