Five suspects have been arrested in connection with the incidents, which authorities describe as the likely work of terrorist groups.
Two men, one of them badly burned, were arrested in Scotland's second city, Glasgow, on June 30 after driving a jeep into the main door of an airport terminal, causing it to burst into flames.
No one was killed in the crash or the fire that ensued. But police say they are treating the case as a "terrorist incident."
The attack came barely 36 hours after police thwarted an apparent plot to detonate two cars in central London loaded with fuel, gas canisters, and nails.
Willie Rae, the Scottish police constable who is leading the investigation into the airport attack, said the events in Glasgow and London were linked.
"I can confirm that we believe the incident at Glasgow airport is linked to the events in London [on June 29]," Rae said. "There are clearly similarities and we can confirm that this is being treated as a terrorist incident."
Police said they arrested two additional people overnight in connection with the events in London and Scotland. They did not provide further details. A fifth person, also unidentified, was reportedly arrested in Liverpool today.
Prime Minister Gordon Brown -- who assumed office June 27-- called on British people to be vigilant.
He also defended the decision to raise the national-security alert level to "critical," the highest ranking and one which indicates further attacks are considered imminent.
"The first duty of a government is the security and safety of all the British people," Brown said. "So it is right to raise the levels of security at airports and in crowded places in the light of the heightened threat."
In July 2005 four British Islamists blew themselves up on London's transport system and killed 52 commuters.