MPs have warned that the preparations for the London Olympics have put the intelligence and security agencies under "unprecedented pressure."
The parliamentary Intelligence and Security Committee (ISC) - which oversees the work of MI5, MI6 and GCHQ - expressed concern that risks were been taken with other aspects of security because of the demands of the Olympics.
Staff have been taken off lower priority areas of work so that they can concentrate on the potential threat to the Games.
More top news
The high of 35C was recorded on a Bakerloo line train between Piccadilly Circus and Oxford Circus at 2pm.
Weather forecasters say temperatures could reach 35C, beating the previous record of 34.6C in the scorching summer of 1976.
After years of political manoeuvring over the future expansion of Heathrow Airport, there has been an important development this lunchtime.