There are a number of well-documented cases of raining animals in modern British history. Such occurrences are not as uncommon as they may sound. With strong winds (thunderstorms for example) small whirlwinds and mini-tornadoes may form. Over the sea these are known as waterspouts, which trawl up water and any fish near the surface. When the tornado touches the land it loses energy and its contents are thrown to the ground. When these tornadoes travel over water any small items of debris in their path, such as fish or frogs, may be picked up and carried for up to several miles.  BBC

Cases

• BBC Overview As recently as August 8, 2000 a shower of dead but still fresh sprats rained down on the fishing port of Great Yarmouth, in Norfolk, England, after a thunderstorm. The fish shower would have been caused by a small tornado out to sea, known as a waterspout, which trawls up water and any fish near the surface. When the tornado touches the land it begins to lose energy and its contents are thrown to the ground.
• Raining animals in the British Isles Excellent “A torrential downpour of goldfish and Koi carp amazed golfers on a Wiltshire golf course. Four golfers, playing on the Netherampton course, took cover in a shelter when it started raining. When they came out, the fairway was strewn with fish”
• BBC report on raining fish “Heavens above – it rained fish in Norfolk on Sunday. Yet for all the biblical resonance of the tale, there is a rational explanation for this rare phenomenon
• 1841: Live fish fell from the sky in Aberdare
• At least four  fish-falls in Scotland recorded in the past 20 years in Fife, Rossshire, Perthshire and Argyll
• Indeterminate creatures fell from the sky in Bath, England, in 1894 ” a storm of glutinous drops neither jellyfish nor masses of frog spawn, but something of a [line missing here in original text. Ed.] railroad station, at Bath. “Many soon developed into a wormlike chrysalis, about an inch in length.” The account of this occurrence in the Zoologist, 2-6-2686, is more like the Eton-datum: of minute forms, said to have been infusoria; not forms about an inch in length”. more here