A Crosman 1377 or 1322 - shoots at 5-6fpe. One of the most powerful air pistols in the UK. Its a multi pump pneumatic air pistol. Easy to charge and would be ideal for the situation mentioned. Pump it up 10 times and leave it. Then cock and load it when needed and it would definitely do the job. Its light and one can be picked up for £50/60 second hand.
Now there's a good choice.
Jim
UBC's Police Pistol Manager
"Nasty, noisy things, revolvers, Count. Better stick to air-guns." Sherlock Holmes, The Adventure of the Mazarin Stone