According to BBC News 24, two car bombs have been successfully diffused in London. I don’t think that is what they are intending to say, but every TV anchor and reporter on the spot is saying this. If it were true, it would mean that the car bombs had been spread out across the capital. What the journalists mean to say, but are mispronouncing, is that the car bombs have been defused.
The two words are frequently mixed up, with defused most often being pronounced “diffused”, but they should be kept clearly apart, as, if a bomb explodes, its contents are diffused over a large area.
defuse: DEE-FEWZ (both syllables equally stressed – almost as if they were separate words)
diffuse: diFEWZ (only the second syllable stressed)