Writer, poet, TV and film producer Henry Normal reckons Spike Milligan changed his life, in particular his 1973 poetry collection entitled Small Dreams of a Scorpion. Spike's other work - The Goons, the books about the war (Adolf Hitler: My Part in his Downfall and Rommel? Gunner Who?) these were important, but it was the poetry that really made Henry think again. Here, he reveals to Matthew Parris what made the one-time Goon so special in his eyes