1996 v6 model..loosing power but managed to get home working through the gears..but allways threatening to cut out..next day would not start at all,and key warning light kept coming on,auto electrician did not have many thoughts about what was wrong..engine turns over but no spark and i cant smell petrol after attempts to start car,hope you can help.

no year, no engine stated, i4 or v6?
the cause is many hard starts
the lamp glowing means get car serviced
or scan it yourself and read the service book on that error or errors, and do the tests stated there.

as far as poor started
THIS is called misfire.
and has 50 causes

#1 is never getting a full tuneup this decade.
ill not list the nifty fifty,
in a shop , they use tools
to conduct tests (engine/spark/fueling)
saving the 50 guesses.

hot starts fail or weak
engine not really hot 180f + themostat bad.
or ECT reads 140 when its 180f actual,ECT bad.
causes flooding that. and hard hot starts.
scan the ECT when hot. first.

Don't shoot me. But this is an old problem. The old polos did the same. I used to drive. Then It would just cut out. Leave it standing for around 20minutes. Start it again. And it runs like there were never a problem. Solution.fuel pump relay. Out of my own experience

Has the fuel filter been replaced recently, if not it could be dirty from crud in the tank jarred loose when the fuel pump was replaced.

as you have'nt said what 'it ' is i'll assume it's newer than 1996 and recommend getting the OBD codes read as a starting point

The codes you can google, but I would say a timing
belt would be a good guess

Can't fix on a guess, have to look & test things

The codes seem like the result of timing being off &
intake & exhaust pressures have an effect on the reason
they came up

Check the anti-theft module and relay

renew the battery its had its day ,it has no reserve capacity because if its old then no doubt its sulphated up.Disconnect from car and put on trickle charge for a week as this may de-sulphate the plates but just renew it ,its not the end of the earth.Also very important with a jag and thats to cleans seats with leather cream and polish the wood .not forgetting to clean the chrome then it work perfectly just like my XJ6 .If none of the above work then threaten it with arthur daily ,english joke a ---dodgy second hand car dealer

most likely its the ignition cylnder (tumbler)

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/sean_54c3a3dc48a7773c

sounds like you are low on gear oil

shift tranny from 1st-3rd if engine revs up clutch needs replacing