OpsR,
You are correct. Anything not declared as a expense will be subject to your tax rate: 22 or 40%, depending on how much you earn. In reality, you will have to fill in the box on your tax return stating how much was spent and the tax man will give you relief on that amount. Unless of course your company enters into an agreement with the IR as already stated.
It is unlikely you will have to produce receipts to the IR, but will need to keep track of them if you are ever audited. The trick is to put in a reasonable number, and the tax man generally leaves you alone.