The Consumer Council has urged beverage shops to enhance their training for staff on bring-your-own-cup (BYOC) policies, adding there was a lack of transparency about such schemes.

Additionally, it also saw cases where paper cups were used to make drinks even when customers brought their own cups, which failed to reduce waste.

The consumer watchdog on Monday said it had sent staff undercover to conduct BYOC trials at 20 beverage shops.

BYOC refers to schemes by drink shops, ranging from coffee shops to hand-shaken beverage shops, which encourage customers to bring their own cups instead of using plastic or paper ones in order to save waste.

Often, this is accompanied by incentives such as a five dollar discount.

Consumer Council CEO Gilly Wong said one problem was shops' inability to properly provide relevant information.

"If you just simply say small, tall, may be standard, normal or similar words to describe the size of your drinks, but unfortunately you haven't provided exact size... then it's very hard for people to follow," she said.

She added that often customers do not know such a scheme exists since it is not consistently displayed, appearing in small letters at the bottom of the poster.

Moreover, problems also arise when staff are not be properly trained, leading to misunderstandings.

"From our findings, there are a couple of times that the shop staff didn't know such offer [existed] and said they didn't have the offer, or missed the discount."

Wong suggested that merchants look into the details of their workflow to ensure the minimisation of waste and to better display their schemes.