Sorry, but there is a huge section of the Great British Public who are quite happy to trundle along at 45 in a 60NSL. It is reality of life. These people are not necessarily driving badly: it is just that they don't have any sense of urgency. They are not being obstructive, they are just going about their business going from A to B in their Transport Modules.
Today I had need to get to Newbury from Wantage. The A34 had, as usual, gone completely tits up, so I came over the downs on the B-whatever. It was a really pleasant drive with bits of 50 and quite a bit of 60NSL, and I could open up and enjoy the drive. But for a lot of people this isn't an option: they are just plodding along doing their thing.
Relax and enjoy your driving when you can, and don't get too frustrated by the plodders, horseboxes, agricultural vehicles that occasionally slow you up.