We are flying from manila to Guangzhou for 36 hours on British passports

No, you cannot. The alternative is to fly to Shenzhen where you can obtain 5 days visa on arrival. Anyway, you should know that with this visa you are limited to the area encompassed by Shenzhen Special Economic zone only.

Anyway, probably the best option would be to go after 144 hours visa free transit. To become eligible for this option, you can take a flight from Manila to Guangzhou and after you stay there for the time you have planned, you can take a direct train from Guangzhou East railway station to Hung Hom railway station in Hong Kong. Like this your itinerary would be Manila - Guangzhou - Hong Kong and this is eligible for 144 hours visa free transit. Please, keep in mind that in case that you decide for this option, you will have to book a ticket for this train online in advance and use exactly that train that you have bought to exit to Hong Kong.