It was just a slow, steady decline. Often just short trip freights, infrastructure trains, light engine movements, plus (mainly) assorted railtours. The last steam movements I photographed around Todmorden & Bolton seem to have been on 26 June 1968, but in early to mid-July, I was on a family holiday in Cornwall.
75019 did a trip working from Carnforth on 3 August, and the last of all (apart from railtours) seems to have been 48519 on a ballast working at Rose Grove on Sunday 4 August 1968.
The unluckiest loco at that period seems to have been Black 5 no. 44888 - specially cleaned and towed to Derby for the Works Open Day on 31 August 1968 - but failed to survive into preservation.