Are petrol driven lawnmowers, hedgecutters, strimmers safe to use in heavy rain

Yes it's possible with LIGHT rain, but as it is today you wont be able to see what you are doing and could slip over and damage yourself with these mechanical tools. Welcome to GOY. Lol.

if it's petrol driven, then there is no electicity so it's safe to use from that point , but slipping could be a problem, especially with hedge trimmers, so i would advise caution ..........steve

Machinery should be ok but safety aspects well covered by above. My only question would be why would you want to ?

Grass would be left in huge wet clumps strimmer would not cut cleanly and your hedge clippings would weigh far more ? Forecast for Wed is good if you can wait.