Spark ignition failure on Canon Chester gas cooker?

The oven spark ignition does not work when the oven is switched on. There is no clicking from the igniter and the pilot light does not light up. Could this be due to an accumulation of greasy cooking deposits, or is it more likely to be a failure of the spark ignition system? How can I repair this? The gas and electrical supplies are easy to turn off to isolate the cooker and the gas baynot connection is easily accessible.