I'm curious as most tiling guides never really specify this point. Do you usually attach the batten with nails or screws?

If screws, do you go trough the trouble of drilling and using wall plugs? If not, are there alternatives?

If you nail it, which nails do you use?

dal - when doing conversions in big London houses back in the 70s & 80s we would fix tanalised battens to brickwork (usually London stocks) with 4" cut nails. These bricks were generally easy to penetrate with these nails; a few 'blobs' of gun-o-prene (an early type of Gripfil) on the batten before fixing. The use of a lump hammer to drive the nails ensured they'd go in after maybe 3 or 4 belts ... using a smaller hammer (say a claw) meant more strikes and could cause batten 'bounce' and result in a loose fix. The beauty of this method was speed of fixing. These cut nails performed much, much better than masonary nails. So as you're in London and if your house is built from yellow London stocks give this method a go. Otherwise use frame fixings.

We drill, plug and screw. Then theres no movement and you can straighten the batten if its a bit bent like most wood seems to be at the moment.