yeah... lots of online tabloid sources for this case. interesting how there aren't any court records concerning it, as the internet detective here pointed out, those sites often don't properly vet their information.
I did try something akin to what you mentioned though. I googled the offenders name. apparently he could have only been out of jail for a matter of months (maybe more with good behavior I'm not sure how it works that side of the pond) before pulling this incident. According to another tabloid "news" site he was sentenced to two years in '09 for burglarizing a little old lady's charity box. along with 3 other robberies. His motivation for these crimes? having no money from being fresh out of jail.
Here's a link to that story It was the fourth link on my google search of his name. the first three were about the incident from OP.
now what made me keep poking around was the facebook and tumblr pages i found for him. they were about as realistic as that random hot strange girl who sends a message every few months asking me to chat, before telling me about some site that's free to sign up for... yadda yadda...
poking just a bit further, I did find one Dacian Martin in Weston-Super-Mare, but the 192.com listing that google found estimates him to be between 41 and 45.
oh and then there were these little tid-bits from the end I found most interesting first from OP article: Man sentenced after head-butting stranger. "Judith Mills, defending, told the court how Martin, who pleaded guilty to the two charges, had never dealt with his parents’ death when he was 14. She added that Martin considered the relationship with Ms Edwards to be ‘destructive’ and now at an end. She said: “Mr Martin lost both his parents at the age of 14 and I think he has not fully dealt with that ever since.'”
and this from the article Weston charity box burglar gets two years from May of '09: "Martin, said Ms Real, [defending attorney in 09] had discovered his parents dead and the heavy impact caused him to turn to alcohol and make himself very unstable."
I'm of the mind set Dacian Martin doesn't exist. The Tumblr SJW doesn't really either. I think tabloid news sites are creating fake identities, to back their fake stories.
and if you think for one half a second her black eye is anything other than makeup, you've probably never had a black eye.