P0303 misfire advice please

Started up to move the car a few yards today and realised there was a misfire - Torque tells me it's P0303, 'misfire detected on cylinder 3'.



I had this briefly about 2,000 miles ago but the misfire cleared after a few miles without the EML coming on. In addition to the P0303 there was also a code refering to low fuel, although I can't recall which one. Codes cleared, all OK



This time the misfire won't clear after running or re-starting, and the EML stays on after a restart/reset - sometimes flashing sometimes steady.



On-line theories seem to range from HT leads through coil packs to lamda sensors so it would be very helpful to know where to start if anyone has had this problem and cured it!



Car is an '02 TF 135, 21,500 miles, 3,000 miles from a complete HGF job (believed also to have included lambda sensor change), no coolant loss, no oil in header tank, oil clean and clear. Running like a dream last weekend!



Any leads or helpfu suggestions gratefully received.

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