What does the cryptic crossword clue "Digger regularly on motorway is a nuisance in Scotland (5)" mean?

The wordplay uses a charade (building blocks). MI (synonym="M1, ‘motorway’") + DGE (synonym="‘ D i G g E r regularly’") = MIDGE The answer is MIDGE.

Digger regularly on motorway is a nuisance in Scotland (5)

Guardian Cryptic #29640 | 16 Across | 2025-03-12 flower