Are you sure that's 1968, Allan? The F1 International Trophy at Silverstone was held in April, and at that point in the season I think the Lotus was still running the high aerofoil which was banned later in the year after the crashes in Spain. This photo shows the later, and much safer, low wing with endplates. I could be wrong - I haven't checked!
BTW in my opinion that season was the high point in Graham's career, not just because he won the championship (and there wasn't a soul in the paddock who begrudged him that), but because of his whole attitude following the tragic death of Jim Clark. He effectively "carried" the team through the rest of the season with his combination of fortitude, determination and depth of character. There was a lot more to him as a person than the joking buffoon he portrayed to the public.