You will never have much luck with halfords and pinecrapple. Ask Wayne or Neal they will tell you that. As said try a local paint place. If not PM Wayne1 he knows of a paint shop that can match it perfect and wayne will probs send it to you if need be.
as said many times. Halfords paint off the shelf is rubbish, you can get it mixed by them, its a little better, but not by much, irrc is around £11 for a small 150ml can. Where as a local auto paint place to me, did a spray can 3 times the size for £8.50, and its a better match. Paint factors are the best places to go, far superior.
Having used to work at Halfords, and mixing the paints myself down to 0.1g accuracy, the match is ****. Although I still continue to use the off the shelf crap because im too lazy to go elsewhere or pay Vauxhall prices.