I guess the nearest we have to part 103 is the Single seat deregulated category
But...you need to have a valid pilots Licence, its only the aircraft that is deregulated
The only category in UK that does not require a licence is the sub 70kg class which consists mostly of powered parachutes and some very lightweight flexwings, I'm not aware of any fixed wing 3 axis aircraft that have made it in that class, it would be no mean feat to design one.
Below is an example of what you can get into the SSDR class with a little imagination ...
https://speleotrove.com/sirocco/G-2DROCO.html