Curtain pole with blown plaster behind

Do you have a photo?

Is it stud wall or dot and dab plasterboard.

 

If its a solid wall, brick or block with a plaster skim or plaster boarded over, then my favourite, bonding plaster will do the job here

Remove all loose and crumbling material, if the hole gets bigger, then so be it, get back to solid background and don't panic. Jobs like this always look worse before they get better

Brush down to remove dust then damp the area to be filled with water, or if you have any PVA, a solution of 1-5 (pva - water)
If you don't have any PVA, you may have a similar, white wood glue which you can use instead with the water (this is my theory only you understand, that this type of wood glue is pretty much pva)

http://www.screwfix.com/p/evo-stik-wood-adhesive-interior-500ml/59593



Mix up the bonding plaster and push well into the hole, 50mm depth in one hit is fine, any deeper, work in stages. Flatten off the area and as the bonding dries, trowel over several times with a damp blade to smooth and blend in with surrounding wall surface

I've found that for small areas and repairs, you can get a way with the bonding as the finished coat as long as you've floated over it several times as drying and blended in with surrounding wall. Once fully dry, its easy to sand anyway so can end up with a really nice, plaster like finish. Mist coat with emulsion to seal and then paint as usual and it "should" be invisible (depending on the prep)

Ready to drill and fit the curtain pole

If a stud wall, then ........ its a different story