It's six months, but only if the fault was clearly present or developing, and not declared to and accepted by the buyer prior to sale, when the car was bought. That is clearly the case here. However, the seller only has to be given the opportunity to repair the fault; he is under no obligation to pay for the fault to be repaired elsewhere.
In this case, if I were to take the car back to Cwmbran to be repaired, it would cost me 260 miles at 30 mpg - at £1.40 a litre (Sainsbury's in Cwmbran), £55 in fuel, plus the cost of a return train journey from Cwmbran to home and back - at best £99, at worst £290, depending on the times, but assume £99 - plus taxis both ends, £20, so at least £175 in total. The seller is not liable for any of that.
The seller has agreed to pay for parts, materials and labour costs as they would be there. Parts and materials cost will be the same whoever does the (specialist) job. The labour cost here is estimated at £300 all-in, and unless his labour costs are less than £125, which I very much doubt, it would cost me more overall to take it there than to have it fixed here. Add to that that I would lose the best part of two days travelling, and it's not just reasonable, it's a no-brainer; I'll have it done here, by a specialist I trust.
