England:
* South East:
* Crowhurst, East Sussex
* Ditchling, East Sussex
* Hartfield, East Sussex
* Mayfield, East Sussex
* Wadhurst, East Sussex
* Horsmonden, Kent
* Lamberhurst, Kent
* Tenterden, Kent
* Tunbridge Wells, Kent
* Dorking, Surrey
* Haslemere, Surrey
* Godalming, Surrey
* Reigate, Surrey
* Westwell, Oxfordshire
* Long Crendon, Buckinghamshire
* South West:
* Wellington, Somerset
* Wells, Somerset
* Crewkerne, Somerset
* Shaftesbury, Dorset
* Weymouth, Dorset
* East Anglia:
* Thetford, Norfolk
* Wymondham, Norfolk
* Bungay, Suffolk
* Lavenham, Suffolk
* Midlands:
* Wellingborough, Northamptonshire
* Market Harborough, Leicestershire
* Rugby, Warwickshire
* Tamworth, Staffordshire
* North West:
* Knutsford, Cheshire
* Congleton, Cheshire
* Yorkshire:
* Skipton, North Yorkshire
* Bedale, North Yorkshire
* Tadcaster, North Yorkshire
* Masham, North Yorkshire
* North East:
* Hexham, Northumberland
* Alnwick, Northumberland
Scotland:
* Borders:
* Melrose, Scottish Borders
* Kelso, Scottish Borders
Wales:
* South Wales:
* Llandeilo, Carmarthenshire
This is not an exhaustive list, but it gives you a good starting point. There are likely many more towns in the UK that end with "well" depending on your definition of "town".
It's interesting to note that the "-well" suffix is often associated with springs or wells, indicating a source of water. Many of these towns likely got their names from such springs, reflecting their importance in the past.