Chase UK are offering 1.5% instant access savings. You have to open a current account first but there is no requirement to pay any amount into current account per month.
Nationwide were also offering 2.5% a while back for existing customers but not sure if still on, and it is limited to £200 deposit per month and lasts for a year so you are looking at around £40 max interest for the year if you pay in the max.
I've moved all my emergency fund money from Marcus to Chase and putting max into Nationwide each month.