You don't need another NC. Download the United_Kingdom_and_Republic_of_Ireland_960_7056, patch the NC and activate the new map. This map you will find in the
Tom Tom Archive-section, tools for patching and activating you find in this section: TomTom Software&Tools
The 64 MB isn't the limited intern memory, its the RAM of the XL. 20,4 MB free is very good. Intern memory should be 1 or 2 GB.