Seems Magpie Securities (through its Magpie Invest app) allows trading in UK securities.
https://www.magpiesecurities.com/zh-HK
Can't seem to find much in terms of pricing and the website isn't in English.
Not going to say recommend this, but its another option for UK trading (although you are probably better of sticking with IB, Saxo or Swissquote).