Triffids?

Whilst we were away these three stalks of "flowers" have shot up from the succulent plants below. The tallest must be over 8 feet tall with a diameter of about 3 inches. They reminded me of the John Wyndham sci fi story of "The Triffids" where giant "mobile" plants tried to take over the planet. Don't know what plant these are but think they are related to the Aloe plant. They aren't very attractive and think I will have to cut them down but it might be easier said than done. Any advice?