It will depend on how they have calculated what the useful life of the stadium is. It's probably similar to the lengths of the loan to pay it. So somewhere between 20-30 years. So if we say that the stadium is useful for 25 years we would be writing off £40m / year (assuming the stadium cost £1bn)I think the player amortisation is set by the length of a contract. E.g. a £50m fee over 5 years is £10m a year.
Depreciation of property developments and other assets is a bit different - you can really decide when to right off the value of stuff, and Spurs obviously have some big numbers to play with if the stadium did cost nearly £1bn.
I'm not an accountant though!

