Actually I think Doctor Who is probably the easiest show to crossover to another franchise. He would fit in anywhere.
Typically an episode of Doctor Who starts with the guest cast, and then about 5-10 minutes into the episode the Doctor and companion(s) show up for no reason. That format would work for anything.
in theory yes, but when you think about it, no.
think about it, all those very public alien invasions, when did that happen in the Law & Order time line? British society in the Whoverse (& most likely the whole of humanity) is very different in the Whoverse than it is in the real world, something that is not seen on Law & Order.
It is bad enough that Without a Trace never refrenced the Cabbie Killer of CSI NY, despite being in the CSIverse, for a show that is apparntly set in the Whoverse not to metion the alien invasions is just crazy.
It's established in Doctor Who lore that alternate realities exist, so in theory The Doctor could
turn up in the CSIverse.
It'd be shit though, so let's not do that.
alternate realities do exisit, but RTDs wasted alternate realities, when he wrote Rose out. The Doctor can not travel to alternate realities now.
As for Martha on Casualty same problem, Casualty has never mentioned any of the Whoverse aliens invasions, besides Casualty has already had a kid wearing a cyberman mask, clearly making Doctor Who a fictional show in the Holbyverse.
never mind that the Casualty set was used in Torchwood: Children of Earth