Aghadowey - I've looked at the 1846 Slater's and the 1924 Pigot's. At present, I don't have access to any others.
Christopher - I've found a William McNerlin who signed the Covenant in Articlave - probably a relative, but I don't know how, possibly my granddad's uncle or cousin. I've also found an Alexander McNerlin who signed in Belfast, possibly my granddad's brother , Sandy. There were 2 more McNerlin signatories from the same address. Granddad was in England in 1912, married with2 kids.