I thought I'd update this as it has now been resolved, from my perspective at least.
Evil's view, based on photos provided by the importer, was that this was impact damage and therefore wouldn't warranty it. My LBS sought a second opinion from a local carbon repair specialist, who believed this was a result of a heavy twisting motion on the rear wheel, with the chain stay being flexed outwards and cracking as a result, i.e. not a direct impact. They also noted how thin the frame was at this point, easily being flexed by thumb pressure.
When the replacement rear triangle arrived, the LBS tested the same area and it also flexed with a "crackling" sound. A second replacement was then sent out - this one doesn't flex anywhere near the same amount so has been fitted.
UK law states that the warranty a customer has is with the retailer rather than the manufacturer. Further, in the first 6 months after sale, it is the retailer's responsibility to prove user damage rather than the other way round. Given this and based on the second opinion, plus the flex on the first two triangles, my LBS have decided to honoured the warranty. At this stage, it's not clear whether they will have to cover the cost.
PS For those suggesting I was stupid for posting a thread before sorting the issue with Evil were right - this thread was cited as "not helping my case" in the initial discussions. Thankfully UK law and a decent LBS outweigh such a response.
