thanks for the replies guys.

The shed is RCD protected and was connected directly to the mixer. The
house is NOT RCD protected and was connected with a 2-wire extension
cable. The mixer was quite old.

I have previously in the past connected electric heaters and power
tools via an extension cable with no problems in my shed, as well as a
kettle etc. The mixer was quite old which could have caused problems.

I am due to pick up my washing machine at the weekend so will need to
connect it up and give it a try.