That is a great pic of Lord Lovat. I love that older than dirt patina that nothing but age and wear can create. That patina cannot be bought and the pattern mixing is very British country.

As to the initial post. If I am going sans tie I normally wear a jumper but I think sans tie with a day jacket looks as good as with a regular tweedy jacket(don't forget a silk in the breast pocket, they are the new necktie). Another option which will make some of you cringe and today(unfortunatly) is a bit of a cliche is a nice patterned ascot. It fits the bill nicely for that country casual look.

Finally, a less over-the-top option that is in between the full turtleneck and ascot would be a partial turtleneck peeking out the top of a button up shirt. If you are prone to overheating like me then buy an inexpensive cotton turtleneck and cut most of it away leaving just the neck part and enough fabric to cover the chest area. It fills the openness of a tieless collar, puts in a casual flair and is more discreet than a silk ascot.