Beware of buying Christmas tree lights from online marketplaces - you could be purchasing a fire hazard, says consumer group Which?
Six out of 13 sets of lights bought by Which? from online marketplace sellers failed a safety test.
Two of them got so hot during testing that they began to melt, while others could potentially cause electric shocks, Which? said.
The consumer group advised shoppers to buy from recognised retailers.
It also bought two sets of lights from High Street shops, which passed the safety tests.
Natalie Hitchins, Which? head of home products and services, said: "Many of the cheap and seemingly cheerful Christmas lights we've tested from online marketplaces simply aren't safe, and we've found some even have the potential to set a tree alight."
Which? urged the new government to make safety a priority and place legal responsibility on marketplaces to prevent unsafe products from being sold on their sites.
National Trading Standards also advised consumers to be careful about where they purchased electrical items.
"It is better to spend a bit more and get them from a reputable trader, than to buy something which could be unsafe and potential cause a fire or electrocution," it said.
Currently, anyone importing an item in order to supply a customer in the UK is legally responsible for ensuring it complies with safety regulations, and could face prosecution for failure to do so, National Trading Standards said.
Which? bought 13 sets of lights from online sellers, of which 12 were either faulty or did not comply with UK standards or both.
Two of the products that failed the Which? tests were sold on eBay, two more on a less well-known marketplace, Wish and two others on AliExpress, which is part of the Chinese Alibaba group.
"In two instances, control boxes on lights bought from AliExpress and eBay got so hot during a short circuit test they began to smoke and then melt," said Which?
The consumer group said both of those sets of lights cost less than £5 to buy.
"The insides were left charred and the printed circuit board was reduced to a molten plastic mess by the end of the test," it added.
"Several of the products also presented an electric shock risk. In an electrical strength test, the insulation in one control box for a set of lights bought from Wish broke down, making the whole unit live, meaning it would be a hazard for anyone who came into contact with it."
Which? said some of the lights were packaged in plain plastic wrapping with no branding or instructions.
Which? said that five products purchased from Amazon Marketplace passed electrical safety tests, as did lights bought from retailers John Lewis and Argos.
However, only one set of lights, bought from Amazon Marketplace, passed all the safety tests and a compliance check.
Online marketplace eBay said it did not permit the listing of unsafe products. "The items have been removed and the sellers advised to contact any buyers with the alert and their return policy," it said
Amazon said: 'All sellers must follow our selling guidelines and those who do not will be subject to action including potential removal of their account. The products in question are no longer available."
Wish has yet to comment on the Which? findings.
National Trading Standards told the BBC that since 2015 its inspections at ports airports and postal hubs have identified over six million items not compliant with UK safety rules, including electrical goods, cosmetics and toys.