Guest, Sinn Fein states, like yourself, that it is the oldest political party in Ireland. This is not strictly accurate.

According to the SF website, it was founded in 1905. It goes on to explain that the name came into use in the early 1900s for a federation of nationalist clubs and that eventually all those to the left of the Irish Parliamentary Party became known as Sinn Feiners.

The Ulster Unionist Party, however, was also founded in 1905.

It seems even the high ground occupied by purists such as yourself fails to straddle both parts of Ireland.