I have had the same problem occur yesterday. Today I have found the oven safety device, mounted beneath a cover on the rear of the oven, has a solenoid coil which is 'open circuit' therefore not energising and allowing more than just a trickle of gas through the safety device. I am trying to locate a new spare online but the first website http://www.espares.co.uk/part/cookers-and-hobs/leisure/p/1092/433/0/0/473705/main-oven-flame-safety-de.html wants £90+ it. Will report back if I find cheaper.
Woody, August 2009