Norway

Winter Season

SAS
Charter (direct) return flight from London Heathrow to Kiruna (All swedish Lapland trips)
Scheduled flights from Heathrow to Kiruna via Stockholm (Any dates apart from charter)
Scheduled flights from Heathrow to Tromso via Oslo (Finmark Tour – start of, and also Tromso and Icehotel – start of)
Scheduled flights from Oslo to Heathrow (Great Nordic Odyssey)
Scheduled flights from Kirkenes to Heathrow via Oslo (End of Finmark tour)

Norwegian Airlines
Scheduled flights from Heathrow to Kiruna via Stockholm, possible to add in a stop over in Stockholm
Scheduled flights from London Heathrow to Tromso via Oslo
Scheduled flights from Kirkenes to Heathrow via Oslo

CONSIDER adding a stopover in Stockholm or Oslo if you wish to extend your holiday.

Finnair
Scheduled flights from London Heathrow to Ivalo via Helsinki (Kakslauttanen)
Scheduled flights from London Heathrow to Kuusamo via Helsinki (Iso syote)
Scheduled flights from London Heathrow to Oulu via Helsinki,
Scheduled flights from London Heathrow to Rovaniemi via Helsinki,
Scheduled flights from London Heathrow to Kittila via Helsinki (Yllas, Lainio Snow Village and Jeris)

CONSIDER including a stopover in Helsinki on either outbound or return journey.

Icelandair
Scheduled flights from Stockholm to Keflavik and Keflavik to London Heathrow (Iceland and Icehotel trip) 

Summer Season

SAS
Scheduled flights from London Gatwick to Bergen (Norwegian itineraries)
Scheduled flights from London Heathrow to Bergen via Oslo (Norwegian itineraries)
Scheduled flights from London Heathrow to Copenhagen (Skane) 

*Scheduled flights from London Heathrow to Oslo (Varmland)
*Scheduled flights from London Heathrow to Gothenburg (West Sweden)
*Itineraries not created yet but hope to be done in the next couple of months

Norwegian Airlines
Scheduled flights from London Gatwick to Bergen (sometimes via Oslo)

Note it is also possible to fly to Alesund and Stavanger