Cracks in Lath and Plaster Ceiling

[Taff in Glaws]

Apologies if this old chestnut has been raised before but I would like some advice on how to fill in cracks on lath and plaster ceiling. There is not much sag in the ceiling but two 'vein' like cracks running for approx 3 metres that vary in width between 1-4mm. Obviously I have been advised to whack some plasterboard over it and skim it but after much browsing of this site I'm determined to use sympathetic materials and not destroy the character of my property.

 

[Lime]

If the plaster is firmly adhering to the laths then repairing cracks is relatively easy.
It is important to clean out the cracks right through to the laths so that a filler can be inserted upto the laths.
I usually use a homemade tool to rake out the cracks. A suitable sized bent screwdriver works well. It grinds away the plaster as opposed to pulling it.
Don't use too much force.
The work can be made slightly less dusty by spraying the crack with water while working. A greenhouse pressure spray works well. I use the spray to clean out the crack prior to filling as well.
An ordinary household filler will surfice like polyfilla. Just make sure it is forced upto the laths.
Next day (don't leave it) sand it down and fill any blemishes.