Certainly for balloon observers, but IIRC the british attitude was that giving a pilot a parachute encouraged them to abandon their aircraft rather than attempting to land it. I believe parachutes became standard issue shortly before the end of the war
the germans had parachutes and there are recorded cases of them being used. However they were not very reliable. I am not aware of the allies using them FNG
If memory serves: All Balloon crew had them. British pilots did not have them, see Ossian's post. German pilots started to be issued them towards the end of the war. No idea about any other nationality.
german pilots had them late in the war ...theres a pic somewhere of herman goering wearing one beside his fokker d7...iirc rfc brass didnt issue them claiming pilots would abandon perfectly good se5s and camels at the first sign of battle damage ...as if skilled ,trained pilots werent themselves a valuble commodity...its been said by rfc veterans that novice pilots were often put in combat so green , that they often froze up and spin stalled to their death in their first cotact and spun all the way down without any enemy bullets even being fired at them ...compared with germany ,france and canada , rfc pilot training was homicide or at least manslaughter writ large..
see this site for a breakdown of recorded jumps http://www.ejection-history.org.uk/PROJECT/year_table.htm FNG