Happened to me as well, only after 700 miles on the tyres, so virtually new. They asked for £12 to fix it, paid £30 as it took them nearly 45 minute, wheel off, remove screw, remove tyre, fix the puncture properly, tyre back, re-balance, re-fit wheel. They're also a bunch of really nice guys, Croxley Tyres in Croxley They used plastic covers for their clamping machine so no marks on the rims.