Remember the Vikings made hundreds of raids, mainly to the North East of England, a 1,000 years or so ago, do you count each of those as an invasion.
The link Zen put to Wikipedia does not seem to include when William of Orange "invaded" England.
Although he had been invited here by protestants to become King of England he was still not sure what he would find when he got here so brought plenty of ships and men.
As it happens he met no opposition and so made his way to London where he and his wife Mary ruled.
But it was still an invasion.
http://en.wikipedia.org/wiki/William_III_of_En gland