@laotou
Thank you. Yes, I see that. I sort of thought that was a insurmountable hurdle too, hence deciding to plump for a British passport and live with renewing visas (my wife and I plan to settle in UK eventually, but not til ma-in-law passes on... could be decades!). Seems that "exit visa" option might not be the guaranteed solution I was after.
Still have to find out how to renounce a nationality that isn't nounced (so to speak!).

The Exit Entry Permit is a seperate document from your sons British passport.

As you are leaving China they look at both documents. Not sure which one they stamp. Then when you arrive in the next country you use the passport.

When you are returning to China you show both documents to get on the plane to China and in Passport Control in China.

I know of a few people who regulary use this document and its quite easy, but at Chinese Passport control a inexperienced officer may have to call his boss over to confirm.

Basically the Exit/Entry Permit is for people who are citizens of China but travel on other countries passports, I guess its only for children as Chinese Nationality law doesn't allow dual citizenship.

Your wife would apply for it where her Hukou is or in Kunming if she is temporarily registered here.

It takes about a week to get.

One negative side of this is if you need to get the fk out of China in less than a week you would have a problem.

@Yuantongsi
Thank you again. I assume then the entry/exit is a once-only document?
If I read you right, the child does not need a Chinese passport to use the entry/exit visa. Do they need to be registred with the hukou?
Sorry for the deluge of questions, but you are a useful resource!!

No need for a Chinese passport.

No need for a Hukou.

The Entry/Exit permit is a once off document.

You just need to apply for it each time you plan to leave China

You also need a foreign (British in your case) Passport.

Ask your wife to call the PSB to see exactly how to apply for a Exit/Entry Permit.

Terrific. That looks like a great option. Thanks again.

"We do not recognize international frontiers." - Daniel Cohn-Bendit

For eneral information/update, what YuanTongSi said above is still accurate.

My school were told by local PSB that my son could get a visa in his British passport, attached to my Residents Permit, BUT the main Kunming PSB refused point blank, because my son is still considered Chinese (born in China with Chinese mother, and despite holding a British passport). The Entry/Exit certificate is the best option for him leaving/returning to China (takes 7 days to get, valid for 3 months). Renouncing his Chinese citizenship is also possible, but I was advised not to start this process until we (my family) had clear plans to live outside of China for some time. Renouncing whilst intending to live in China is seen as a bit suspect and the application can be refused (or is accepted and the consequent visa application is refused). Again, YuanTongSi was spot on.

The most frustrating thing was it took 3 weeks, lots of paperwork and (believe it or not) a "required interview" with my 7 month-old before we were flatly refused. Thankfully, after some moaning, a PSB officer with excellent English was able to explain the reassons and give advice on next steps.