Hi to you from David. In answer to your question, YES it can be repaired. Basically the control knob for your oven is faulty. When you turn on your oven, the pilot lights as normal but flame stays small, this is because the FSD as it is known (Flame Safety Device) has failed. To correct this fault you will have to have this replaced. The cost of the FSD is usually around £40 plus of course the fitting charge. A Gas Safe engineer is required to fit this for obvious safety reasons and you can expect to pay £50 - £85 for his services.Hope this helps with your decision. Just in case your probe has moved, if you look in the oven , you will see a probe, just above the pilot flame, ensure this is still in position, if not try repositioning and you may be in luck. Chance of this, 50- 50. Best of luck regards XXXXX XXXXX much appreciated.
Many thanks - this mirrors the advice I found later on another website about cooker problems.