Brief Stop in Guangzhou/Hong Kong

Hello,

I am travelling from the UK to Singapore in March. On the the way out we have a stop over in Guangzhou. Our flight lands at 18:30 and we are plannning on getting the train to Hong Kong for the night. We are then flying out of Guangzhou to Singapore the following afternoon (around13:00 therefore will be in China for over 24 hours. Please can you advise what the best visa is for Guangzhou/Hong Kong stop over?

On the way back we are staying less than 24 hours and will not be leaving Guangzhou therefore should be able to get the '24 hour stay permit' - is this correct? I am a UK citizen and am flying to Singapore for a holiday.