THE very first ha-ha does not refer to the congregation’s response on discovering that its minister has finally, after 30 years of preaching, uttered a jocular remark. Instead, as we learned in the first episode of The Secret History of the British Garden (BBC2, Sundays), it is the earliest example of such a feature, at Levens Hall, Cumbria.

A ha-ha is formed by a dry moat that gives the impression, from the landowner’s side, that his garden stretches to infinity, yet to the picturesque herds of cattle and deer on the far side, it presents an insuperable boundary, hindering their approach to the house and garden, to the point at which they would become significantly less picturesque.

It is a perfect model of what we want from horticulture: the impression of wild nature, linking us with the rest of creation, while at the same time ensuring that we are not incommoded by the discomforts and challenges of nature’s reality.

Monty Don is a first-rate guide, and he led us on a journey — ideal viewing for a winter Sunday’s post-evensong viewing — through the development of an art form where, as the Renaissance took over from medieval sensibilities, intellectual delight and stimulation was thought more important than mere beauty.

At Lyveden New Bield, an unfinished Elizabethan summer-house in Northamptonshire, every aspect of the design has a symbolic meaning that proclaims its owners’ Roman Catholic allegiance. Formal planning spoke of the victory of human rationality over the wilderness of a fallen creation.

How Britain Won The Space Race (BBC4, Monday of last week) might seem to be an irredeemable fantasy, but proved to be, with the second half of its title, The Story of Bernard Lovell and Jodrell Bank, none other than the plain unvarnished truth. In the first years of space exploration, the remarkable radio telescope was the only instrument on earth capable of tracking Russian and American rockets and satellites. Both sides knew this, and both sides relied on its evidence for their achievements.

This had an interesting effect on Lovell: the media and political attention meant that, at last, he got the funding to run the telescope properly; but the external pressure to divert attention away from the pure research for which it was designed, to something far more basic, led him to a breakdown.

The programme considered that the acuity of his condition was demonstrated by the fact that this lay-preacher’s son thought of giving up science and being ordained.

This was a terrific story, told as an example of British pluck and determination, creating out of post-war scrap a world-beating facility, mapping for the first time phenomena beyond the visible spectrum, in the intervals between playing cricket and practising the organ.

I have come to the series River (BBC1, Tuesday of last week) just as it is ending. The final episode was magnificent: every twist and turn of revelation turned back in on itself, darkening and illuminating our understanding of each character. The implausibility of the story was trumped by the reality of its protagonists.