David, the '68 manning agreement had more conditions than those I and Ken W have alluded to. For example there were restrictions for single manned turns on distance travelled non-stop and number of hours continuous without a break - for KX men any first stop Doncaster or York runs may have breached either or both of these conditions hence needing a secondman, and these could have been the turns you accompanied your Uncle on, especially if he was in the Top Link.