Do you get a pilot light or any sign of flame during the ignition sequence?
Based on the age of the boiler, and the likelyhood you are now at a point of changing parts until the fault clears, I would strongly suggest you replace the boiler, as it is a case of good money after bad.
Another option would be to go for a repair and protect plan, I believe British Gas offer a fixed price repair for around £250, which includes all parts, labour and then a full years warranty, if they attend and cant source the parts there isnt normally any charge.
So I may resolve the case and receive payment from Just Answer for assisting you, please could you rate the service received.
Please do get in touch if you have any further queries.