cryptogram, Welsh-like morphology, language game, nonce phrase.
Alternatively, it may be an intentional jumble of “The mill by the old land road, my dear fair” with heavy metathesis and Welsh influence. The phrase shows no systematic cipher or standard language. It is best classified as pseudolinguistic play — possibly a mnemonic, a constructed code, or a corrupted line from a fantasy work. Future work may involve testing against large language model embedding spaces.