The original Regan blurred the lines a bit strictly so he could nick people.
Ray Winstones Regan was exactly the same, but in a very modern, more gritty way. He cheated, stole and bent the rules to breaking point; but he did so with the sole purpose of putting the real crooks behind bars.
He might skim a bit here and there for his troubles, which in the eyes of the law makes him a crook himself, but he sees it more as getting a little bonus, "the stolen goods are likely covered under insurance anyway" mentality. I feel compelled to use the definition of Chaotic Good from D&D to best describe his portrayal in the movie
A chaotic good character acts as his conscience directs him with little regard for what others expect of him. He makes his own way, but he's kind and benevolent. He believes in goodness and right but has little use for laws and regulations. He hates it when people try to intimidate others and tell them what to do. He follows his own moral compass, which, although good, may not agree with that of society.
To quote the start of the film directly (just after the raid on the warehouse)
"Yep, nice work regan, but did you really need to destroy the whole place in the process?"
Regan: "We got the villains didn't we?"
Well i've got the headache of explaining why you smashed their heads in and wrecked the whole depot!
Regan: "We got the villains didn't we?"
..... Regan: "You get internal affairs off my f'ing arse, and I'll get you results"
The internal affairs investigation doesn't really go away, but the ingots being stolen scene set the tone between Regan and Frank Haskins for the rest of the film. As Haskins wants to bring Regan down for all the crimes he's committed but just hasn't got the evidence to make good. He KNOWS Regan is bent, and Regan knows that, but doesn't care becaaause (say it with me now!) "We got the villains didn't we?"