It is entirely possible that you can make a loss on a rental property, for example if you had a lot of problems with the property or you offered a rent free period.

The tax man does have a heart.  If you own a rental property that made a loss you will not pay tax for that particular tax year and you can carry the loss forward to later tax years and set that loss off against future profits.

If you own more than one property, then you must accumulate all the profits and losses on your properties for the tax year so any losses are automatically used up.  You can’t pick and choose how you use or carry forward your losses!