A modified version of the DigiKeyboard library configured to work with UK layout keyboards.
The only difference is the mappings in the scancode-ascii-table.h file.
Simply add a folder to your Arduino's libraries called DigiSparkKeyboardUK (though I believe anything will do) and deploy the files in it. For most users, this ISN'T in the software installation folder but rather a folder in their user profile such as:
C:\Users\YOURUSERNAME\AppData\Local\Arduino15\packages\digistump\hardware\avr\1.6.7\libraries\DigisparkKeyboardUK
Include the library in your project using #include "DigiKeyboardUK.h" and then follow any of the tutorials for the standard DigiSpark.h library.
An other option for those ONLY compiling for UK keyboards is just to overwrite the scancode-ascii-table.h file in their existing package (though obviously if an update is pushed out for the library it could well get overwritten.
Have the library added to the online respositories so it can be installed via the GUI in the ARDUINO IDE. Make some pretty pictures showing the key differences. :-)