Harry Bloomfield wrote:
Dave explained :
I bought one of these little rascals that help you to do mitres in
the stuff http://tinyurl.com/yzhmpor (link goes to Axminster tools)
but what's the best implement to actually cut polystyrene coving
with? Wood saw? Hacksaw? Bread knife? Something else?

It cuts cleaner with a hot wire cutter, but failing that hacksaw or
bread knife using a gentle sawing action.

Thank you very much Harry - the only person to actually answer the question
I asked.

I know plaster/Gyproc Lite coving looks, and indeed is, better but (a) we've
got a huge amount to do and the budget won't stretch that far and (b) we've
already bought the polystyrene coving because that's all our budget would
allow.

Regarding the fire risk and polystyrene - we have no kids, we don't smoke
and the house was recently rewired so I think we could be classed as a
low(er) risk household. However, just in case a fire should break out, we
have mains operated (battery backup) interlinked smoke alarms in almost
every room (and an emergency light in the hallway and on the landing wired
into that circuit that provide indication of mains failure), so I reckon the
risk of polystyrene coving is an acceptable one.