I'd go for a timber batten on 3 edges to support the desktop from the wall. Reason: drilling into tenement walls can be unpredictable. A batten means you have multiple fixings and if one is duff the rest carry the load. Using shelf brackets like you're suggesting surely can work but puts more pressure on your DIY skills. Maybe/hopefully you're better at drilling holes in walls than me :)
I'd go for a timber batten on 3 edges to support the desktop from the wall. Reason: drilling into tenement walls can be unpredictable. A batten means you have multiple fixings and if one is duff the rest carry the load. Using shelf brackets like you're suggesting surely can work but puts more pressure on your DIY skills. Maybe/hopefully you're better at drilling holes in walls than me :)