The Anglo-Saxon invasion of England is always portrayed as a naval invasion using ships very similar to the later viking ships. According to "Vikinger i Krig", the use of sails is likely one of the development that triggered the viking raids on Europe. If this is true, why did the Angles, Saxons, Jutes etc have access to this technology long before the viking, despite using otherwise very similar ships?
That's still an unsolved mystery. The few ships we have from this period are ambiguous (they might have had a mast, but we're not 100% sure). Romans had sails, though, and sailing ships were pretty common for merchants during the late 7th century. However, deep into the Viking age warships and personnel carriers were primarily rowed vessels (because if you have lots of guys, might as well put them to work). Cargo ships have more of a manpower/size concern, so it is likely that the sail was more readily adopted for this purpose.
Anyway, it is a bit nonsensical to think of the Anglo-Saxon invasions as a Normandy-style (either one actually, both 1066 and 1944) naval landing in the late 5th century. Rather, most immigrants would have come piecemeal in rather small units (households, single men, basically the same as modern migration) on probably Roman ships during the 4th century already. That said, it is not impossible that there were relatively small groups of warriors coming over as an army during Late Antiquity as well; it is likely that if they did not use Roman boats, they would have used a rowed Nydam-style vessel, or something similar to the Sutton Hoo ship.
I earlier made another AngloSaxon Invasions-post here.
Anyway, why the sail was not adopted in Scandinavia before the late 8th century (to spark the Viking age), one reason is that shipbuilding is inherently conservative. People trust their lives on a piece of wood, with no modern understanding of the physics involved, and everything being based on experience and skill. It is very easy to mess things up when you concentrate the force of wind on a ship if you don't know what you're doing, so if I were a Scandinavian from the 8th century, I wouldn't trust my life on what is basically an experimental piece of technology. Besides, you don't really need a sail if you're out raiding, as you row along the coast anyway (it's also more reliable to row, less dependent on wind conditions). So the lack of big sailing ships for military purposes does not imply that the use of the sail was unknown in Scandinavia, but rather that people chose not to use this technology. The turn of the 9th century thus is more the point where the sail was adopted, not the point where it was invented/introduced.