Uk passport, HK>Guangzhou>Macau>HK

Your itinerary is good, but you cannot use the train to enter Guangdong province! The only eligible way to enter Guangdong province, while using 144 hour visa free transit, is by taking a flight. In other words, you would be eligible for 144 hour visa free transit valid for entire Guangdong province, but you should fly into it. You can fly from Hong Kong to Guangzhou instead of taking a train.

As far as your exit from Guangdong province to Macau is concerned, the best option is to take a direct ferry from Shekou port in Shenzhen to Macau. You should be aware that you will have to obtain a ticket through TurboJet website for this ferry even before your departure from Hong Kong. You should print it out and have at hand, ready to present it to the relevant authorities. Also, you will have to take exactly that ferry you have bought your ticket for.

Thanks Borut, my wife has since found out that the ports have been updated WEF 15th July.
We can do this route instead: HK>Guangzhou via ferry entering China at Nansha Port. Then leave Guangzhou by train to Zhuhai (Macau) and then ferry from Macau to HK. This should be ok for the 144 hour visa rule. In which case, we need to have booked in advance the train from Guangzhou to Zhuhai for inspection before 144 hr visa. Many thanks

David, I advise you to be very careful because none of the announced ports like Nansha and Shekou are yet introduced into Timatic database and Timatic is, as you know, the basis of every single border official in determining whether someone is eligible for some travel in/through some country or not. In other words, you will risk in attempting to leave Hong Kong toward Guangdong province in order to enjoy 144 hour visa free transit scheme. It is undoubtable that those two ports will be eligible for such an option, but so far you can encounter problems because Hong Kong border officials are not yet aware and they even cannot check that at Timatic as relevant data base. In other words, you run a risk not to be allowed to exit Hong Kong toward China, especially toward Nansha because you can always justify your departure toward Shekou because this is the place where Shenzhen VOAs are issued. To conclude, please, be careful.

Another detail that is definitely not possible is to take a train from Guangzhou to Macau. The reason is simple. There are no direct (through) trains from mainland China to Macau and you need a through mean of transport, obtained in advance in order to be eligible for 144 hour visa free transit. Trains from Guangzhou toward Macau stop at Zhuhai train station just a couple of hundred meters before Macau, but do not enter Macau. The alternative is to take a ferry operated by TurboJet from Shekou to Macau or by taking a through bus operating from Zhuhai airport to Macau. These are the options where you can buy the ticket in advance and that such a ticket is eligible for 144 hour visa free transit option. I am not aware of any other option at the time being. Again, you need all those tickets obtained in advance.