No it is not and I do not really think that you believe that I am.
A letter from E-I stating what had happened together with the relevant log entries would constitute a complaint that would have to be considered. Then the computer crime folks would approach BT and ask for the logs for the IP address and the ID of the subscriber. The evidence of those logs might then be used in court. Indeed, I would expect that the UK computer crime folks would be a lot more interested in the BT logs as they would then be able to see what else the purported miscreant had been up to.
(I say BT because, before the posts were edited, the IP address of the reported attack was visible and a lookup indicated that the address was in the range used by BT for their broadband customers.)