Thanks for all the helpful replies, particularly Lady Muck. I've already made money leaving journalism and doing property development by doing just that - hiring builders and doing a bit myself. I don't think you have to find something no one else is doing to set up a business, otherwise there would only be one of each type of business in the world.
Anyway, I wasn't really asking for general business tips, just about whether or not these two options were feesible. Looks like maybe not. Thanks anyway.
As for Dragon's Den, I hate that bloody programme.