From my point of view, I honestly don't think it will help (though that depends on what you're hoping to get out of it) - mainly because those few MP's/advisers with an interest/responsibility for adoption are aware of what's going on given that this situation has been ongoing for well over a year, and other MP's can't really do anything useful (IMHO) other than raise their consituents issues with them. The drop in the number of placement orders being issues is partly a court issue, which is outside what an MP can address. That said, I don't think there's anything wrong with writing to one of the couple of people who would be interested (Martin Narey? Edward Timpson?), as long as you're clear what you're hoping for and have a realistic expectation of the likely response - it won't be a change, but maybe if you were wanting to make them aware of how things are working in your area right now, and get a probable reply saying they got your letter, and they are trying to address the issues raised, and have done x recently. That's my take on it anyway.
Side note, if I were writing to Narey etc, I would be asking why agencies are still being encouraged to recruit new adopters given the current climate. No, to other posters, it's not just about babies, the number of children waiting for adoptive homes is lowered very significantly across the board, whether older or younger, disabled or healthy, single or siblings - and given the continued cuts etc over the last few years, I would have thought it would be obvious that it isn't because fantastic support services have suddenly materialised which are enabling some children to remain with their birth families. The pendulum is swinging as it always has - towards more adoptions, then less, then back again, and again...who knows what will happen now. Either way, what will cause a child to be adopted in one year is not the same as in 5 years or 10 years - which doesn't say anything very good about the system.