Great Britain Speedy Letter Service 1971

I am not sure if this belongs here or with the Cinderellas. This sheet fell out of the a beginner's Harris album I just fanned through. I understand that these came into use during a Great Britain postal strike in 1971. The right side of the sheet is cut so clean I am wondering if it was printed like that or maybe there was an imperforation down the middle of a larger sheet that was then split. I see singles and small blocks listed on eBay at low prices so no great treasure but I guess I will keep it because I really need more stuff...