Property income loss and pension adjusted Income

[someone]

If I make a loss in a property business for 2017/18 (due to starting to let right at the end of the tax year) I understand that I cannot use that loss to offset against other income but have to wait to offset the profits in the next tax year.

But what happens to adjusted income for pension tapering? Does the loss get accounted for in the year it occurs or in the year it reduces the taxable income?

I'm assuming it will be the second - that the loss reduces the adjusted income in the year that it is used, not the year that it occurs.

Otherwise, in extremis - someone has 210K employment income and starts up a property business with 210K losses. No pension tapering. Next year having given up employment property business makes 210K - full pension tapering but no taxable income.

Of course, they could count it twice! (No I don't really believe that)

In my particular case, using the loss in the next tax year to reduce adjusted income will be most tax efficient. Can I delay claiming any of the startup expenses until April or do I have to claim them on day 1? (Letting hasn't actually started yet but the agent said it would be before the end of this tax year. I will make a healthy profit by the end of the following tax year unless something goes very wrong)

[someone]

And I've found the answer to my last question in PIM2505:

Qualifying pre-commencement expenditure is treated as incurred on the day on which the customer first carries on their rental business. This is deducted, together with the other allowable expenses of letting, from the total receipts of the business for that year.