Are there nonstop flights from London (LHR) to Skiathos (JSI)?

No. The fastest connection is via Venice, about 3h 42m of total flying time.

What is the fastest connection from London (LHR) to Skiathos (JSI)?

via Venice ≈ 3h 42m, via Zurich ≈ 3h 43m, via Basel / Mulhouse ≈ 3h 43m (estimated flying time, excluding layovers).

from 15,000 ANA miles (economy, one way, based on the published award charts).

London Heathrow Airport (LHR) to Skiathos Island National Airport (JSI)・2,302 km

No nonstop flights. The fastest connection is via Venice (VCE), about 3h 42m of flying time (layover not included).

With milesANA 15,000 miles+ (via VIE)Economy, one way, estimate. Tap a connection for miles by cabin.

None.

20 one-stop options, sorted by estimated flying time. Tap one to see the airlines on each leg and booking links.

Times are estimated from distance. Check schedules, frequency and availability with the airline or a booking site.