Was there a Norman/Viking conspiracy to attack England in 1066?

Listener Shane asked if William the Conqueror and Harald Hardrada had an agreement to attack England jointly.  This could after all explain certain curious behaviors by both William and Harald.  The Duke delayed his departure to England claiming a lack of favorable winds- was he instead waiting for Hardrada’s attack to draw away King Harold’s forces?  Along the same vein, did the Norse invader lower his defenses after Stamford Bridge because he was expecting Harold to be tied up at Hastings?  The Normans and Vikings had deep ties and a shared cultural background and it isn’t beyond the realm of possibility that they would act together.

It’s an intriguing idea, but ultimately, I think unlikely.  While the close timing of the invasions was certainly mutually beneficial and Hardrada almost certainly knew of William’s plans (he hardly bothered to keep them secret), neither man’s personality was given to sharing.  William genuinely believed that he had the best right to the entire kingdom, and while his delay in crossing the Channel proved fortuitous it would be giving him too much credit to say that it was a calculated strategy.  Every day that passed with his army still in Normandy cost him in money, food and reputation, and he was as anxious as Harold to resolve the situation as quickly as possible.  The more opportunistic Hardrada may indeed have taken advantage of William’s threat, but he was no more likely to share authority than his Norman opponent.  He had just finished a fifteen-year war with the legitimate king of Sweden, fought for no other reason than a blatant power grab.  This was a man who clearly didn’t tolerate rivals.

If indeed there was an agreement- something like the partition of England that Cnut and Edmund Ironside had concluded a generation earlier- it’s interesting to speculate what would have happened.  It would clearly have been a partnership headed for disaster, as neither man would have trusted the other an inch.  Only a matter of time and they would be at each other’s throats.