My wifes beetle ,a 1971 stock ,runs very poorly when cold
She says it chogs and backfires constantly and can onl;y travel about 15km an hour
Once warm everything is fine
but takes about 10km to warm up
Has anyone got any advice please

CHECK the choke on the carby

Definatley check the choke on the side of the Carb. Make sure it is connected electrically still.
Turn the ignition on, but dont start car, take air filter off top of carby and have a look down the middle of carby. If the plate/butterfly is pointing up ( so you can see deep down into carby throat) the automatic choke isn't working. If its flat and blocking off the carby throat then its started its cycle. Wait a about a minute or so, floor the accelerator (still with engine off) take foot off and go and have another look. If you can now see down the carby, all is good with autochoke.
Might be worth checking your distributor cap and rotor arm too. They are cheap to replace, but as they wear they tend to hate the cold damp mornings, trust me, i'm a pom so that means 340 days per year over there!!
Good luck.