In reply to Steve Grant.

Hi Steve, the 3rd party Block Install you mentioned is called the Block Directory. You can disable it with these lines of code:

remove_action( 'enqueue_block_editor_assets', 'wp_enqueue_editor_block_directory_assets' );

remove_action( 'enqueue_block_editor_assets', 'gutenberg_enqueue_block_editor_assets_block_directory' );

Here's a link to the docs: https://developer.wordpress.org/block-editor/reference-guides/filters/editor-filters/#block-directory