The man, in his late 40s, was involved in a housing dispute with bailiffs at the property on Stapleton Hall Road in Stroud Green.
Police officers were called to the scene at midday after receiving reports the man was armed with a weapon.
Shortly after they arrived the explosion took place, leaving him with severe burns. Three police officers sustained minor injuries.
The basement and parts of the ground floor and shed in the back garden were on fire for several hours. No neighbouring houses were damaged.
The cause of the explosion is not yet known and there have been no arrests. The Met said it was not looking for anyone else in connection with the incident.
Witness Paul Pixton tweeted: "Something massive is happening on my street, some kind of altercation on street followed by loud explosion."
A man has been critically injured in an explosion at a house in north London.