Office Space in Client's Office

One of our clients has agreed to allow us to use some of their office space gratis whilst we get to our feet.

Is there anything that we should consider that may not be obvious. I'm aware that we would like some kind of agreement to ensure they can't pull the rug from under our feet instantly, however I'm wondering whether there are more subtle issues such tax or legal considerations.

If it's applicable we are in England and if there are any legal considerations could they be localised as such?

One of the biggest things I would make sure to cover up-front is that you are "renting" this space (you should work out some kind of specific terms), not acting as their on-site support and suggestion department for the product.

This is the sort of scenario that could work out really well for you, or could end up as the kind of situation that you end up dreading going into the office because you know you are going to get slammed by a ton of requests from them.

I would take time to spell out the terms of the "lease". EG: in exchange for 4 desks, access to the coffee pot and your own keys the client gets Y weeks of free service, future upgrades, etc.

Doing this purely as a hand-shake deal could lead to small or large problems later.

Other things to cover would be use of shared resources (copiers, conference rooms, etc.). Handling of guests (will their receptionist be aware of you and able to deal with guests, should you have any?), access to the office outside of normal hours. Specific area(s) that are "yours" for the term.

I'd clarify a few things in writing, just so the rules don't uncomfortably change over time:

1. The terms of your stay so there are no surprises (Length, rent, access, shared resources etc.)
2. Does this change your legal relationship to the client? In the US (I have no idea about the UK), working at a client site can, under certain circumstances, cause you to legally be viewed as an employee. This has all sorts of implications, including taxation, benefits due to you, and ownership of any IP you create while 'under their employ'.