It's like we've switched places!!!! I grew up in Michigan and am now living in the UK.
There are definitely differences between the market, though sometimes these differences seem intangible and hard to categorize. There are also different trends. Actually blogged recently about how big historical fiction is in the UK, where it's not really so big in the US. The US market is definitely bigger, so I think there are slightly more opportunities there, more agents to query, more publishers to consider, and more opportunities... like I think tween novels are possible in the US, whereas in the UK they're still kind of a non-genre. But on the flip side, the smallness of the UK market means it's easier to meet people, and I have found more opportunities publishing wise (instead of competing against 4,000, for example, I'm competing against 40).
There are several agencies I have found which have agents on both sides of the pond. Greenhouse Literary springs immediately to mind, but there are others.
So nothing too specific, unfortunately. I'm just beginning to get a feel for it myself. I would look into the area you're particularly interested, in both countries, and see what you find.