Corporate flat rentals is located in virtually every town in North America and a number of other areas around the globe. What's the distinction between a company and another kind of rental? Not that much difference, in all honesty.
The basics are the same – a suite of rooms in a building which includes at the very least a bedroom and a bathroom, which may be private or sometimes the bathroom is shared. You can choose contractor accommodation in London through the internet.
If it is advertised as an apartment, you should expect that there is also a kitchen and some sort of living room, which also may be shared with other guests in some situations. Because it is advertised as "corporate," it should also include a desk and wireless Internet access, and possibly other business tools such as a scanner and/or printer with all the necessary connections.
The apartment should contain everything you need to conduct business from your temporary home, plus a comfortable place to relax and unwind when your work day is done.
Note the words "temporary home." This is what a corporate apartment is intended for, to be a home-away-from-home for business people who need accommodation in a different city or country from time to time.
They are meant to be temporary rather than permanent arrangements, although most will consider both short term or extended stay situations. This could mean anything from one or two nights to two weeks, a month, or six months or more.