I think this is normal to be honest: a large loss at the beginning (12lb is amazing - congratulations) followed by a steady but much lower rate moving forwards. I've just re-started but (after first week) I usually lose between 2 and 4lb, but definitely no more than that (and far more often 2 than 4).
I know it can be a bit disheartening because you feel like you want to lose the weight as quickly as possible but even VLCDs don't work like that. They show measurable and encouraging losses (which is why I prefer them to other types of diets) but they're not a miracle pill.
The other thing I sort of tell myself is that weight loss isn't a race. While it's really helpful to be able to see other people's successes, everyone's body is different and so you can't really compare yourself to what is going on with someone else, or let yourself get frustrated because you don't work the same way. These things take as long as they do and it's better, if you can, to settle into that. After all, you're here for the long haul, right?
Another way of looking at it is that even at this rate you'll still lose about half a stone a month. Which means in six months time you could be THREE STONE lighter. That's a huge amazing fantastic difference. So I'd say, don't worry and stick with it. And you've still lost 19lb in a month. That's really, really good. *cheers for you*
All of which said (sorry, I'm super long-winded today apparently): have you done any cheating, because it really does make a difference. What are you drinking? Exante allows coke zero and similar, I think, but I tend to cut out all that stuff. Are you getting enough water? That, too, can have an impact (for whatever reason). Finally, while you shouldn't exercise on a VLCD because you're already on a ludicrously low amount of calories, I think some gentle walking can also be good.