It's impossible to answer that question without knowing how you intend to book and which price you go for. If you book direct you are likely to be offered a number of options by Accor's system, some of which are penalty-free, some of which are no-change, no-refund and some of which fall somewhere in between, such as ones that are penalty-free if you cancel some days in advance.

If you use a deal such as the lastminute.com offer which many were talking about in another thread here, then you'll see that the charge for cancellation is one night's stay. In other words, that is effectively a deal with no refunds unless you are planning to spend multiple nights at T5! (The lastminute.com offer expired yesterday, I think, though some have reported that you can still get a good price through them though not as low as £88.)