Police found the devices by chance when they searched the property in Langley Green, Crawley, West Sussex, on Tuesday evening as part of an investigation into an alleged fraud.
Though crude, the bombs were ready for use, and police called bomb disposal experts.
The discovery raised fears that the devices might have been part of a terrorist plot. Neighbours said yesterday that the men once worked at Gatwick, which is less than five miles away.
However, police sources said yesterday there was no evidence so far to suggest the men were part of a terrorist group, or that the bombs were to be used against a specific target.
Scotland Yard's anti-terrorist branch said that it was liaising with Sussex police, but there were no plans for its officers to become directly involved in the inquiry.
The men being questioned are European, possibly Portuguese, and are aged 41, 38 and 35. They are being held under the terms of the Terrorism Act 2000.
Inspector Geoff Sharnock of Sussex police said: "During a routine inquiry, two viable improvised explosive devices were found.
"Three men have been arrested. One was arrested elsewhere and two were arrested at the flat."
Police said 25 homes and shops had been evacuated while the area was examined.
