I have now completed the Lea Valley Walk, from the Thames to the source at Leagrave. Three full mornings and two half-mornings for 93km, of which 44km was an unbroken stretch on towpath, 14km was on railway trackbeds (much of which was tarmac), and the bulk of the remainder on urban roads and paths.
For these reasons, and paying attention to the complaints from my heels, it will not feature in my top ten routes for through-walking. It is perhaps more suited to accumulating coverage, jigsaw fashion, as part of day circuits.

There are many points of interest, from the view of Bow Locks to the peek across the valley to Luton Hoo (landscaped by Capability Brown). But I longed for a bit more variety between Bow and Hertford, other than the “water on the left” and “water on the right” sort of variety.

The driving rain I met on the last half-morning was not conducive to thinking well of urban Luton, though the rain eased off just before I reached the source.