Inspector Heat is a cop who loves the thrill of a good ol' manhunt. He doesn't even dislike criminals, but thinks of them as necessary to society:
Thieving was not a sheer absurdity. It was a form of industry, perverse indeed, but still an industry exercised in an industrious world. (5.36)
In other words, Heat thinks that thieves are just as honest and hardworking as everyone else. It's just that their job involves a different set of risks than, say, making cabinets. This would've been a really scandalous thing to write in 1907, and cheeky Conrad wasn't a fool: he knew that. People at that time thought there was a super clear line between citizens and criminals, and if there's one thing Conrad loves to do, it's tear down boundaries. He doesn't do this just for the sake of messing with people, though. For him, things are pretty simple. If you've got a world where a huge group of people don't have enough to get by, and a small group of people have way more than they need, you're going to have thieves. That's just simple arithmetic.
Heat has risen pretty well in the ranks of the police force. He's good at his job, but he's also a bit corrupt in the way he likes to do things. For example, he prefers to use Mr. Verloc as his own personal wellspring of information and keep Verloc a secret from the rest of the police. Also, he's perfectly happy to send a compassionate man like Michaelis to die in jail for a crime he didn't commit, just for the sake of making a neat and tidy case against a known anarchist.
Heat's personal way of doing things comes through even more clearly when he takes a major clue (the piece of fabric with Stevie's address on it) from the human remains found in Greenwich Park. He also tries very hard to convince Verloc to escape from England after the bomb outrage, since he still has a lot of use for a man like him, and he doesn't want Verloc tearing down all the spy networks he's been happy to exploit for years.
But like every other character in The Secret Agent, Heat has a blindspot: his love of rules. Heat's pretty well-adapted to the modern world because he's willing to treat life as a game. But his insistence that people follow the rules of that game is what makes him weak. He has no clue how to deal with someone like the Professor, who just wants to create chaos in the world. Actually, one of the most notable things about Heat is how much he hates the Professor, because:
Catching thieves [...] [has] that quality of seriousness belonging to every form of open sport where the best man wins under perfectly comprehensible rules. There were no rules for dealing with anarchists. (5.61)
Heat is a man who loves to catch criminals, but he's stereotypically British in the way he wants to do his job according to a very strict set of rules. But, despite this weakness for order in a topsy-turvy world, you could argue that Conrad actually paints Heat as more likeable than most of the characters in The Secret Agent.