Mercifully not preceded by a Broadchurch-style hype-tsunami, the new series of Mr Selfridge has slipped neatly back into the Sunday 9pm slot as if it's the rightful owner just back from a year of travelling round the world. It's not revolutionary, ground-breaking or "subversive", but equipped with some new characters and promising plotlines, this opening episode ushered us into the post-World War One era with a spring in its step and the wind in its hair.

You can see why writers and TV companies like the idea of creating sequels to successful series, but trying to make lightning strike twice has obvious drawbacks. In the case of the original Broadchurch, the runaway ratings blockbuster which ended in April 2013, the story felt so complete and self-contained that the notion of a sequel seemed redundant, or gratuitous.

“But I do want to be stuck with you.” Five series and five Christmas specials down, Downton fans heard a line of dialogue they had no idea they’d been waiting for all this time. Never mind that the scenario was a straight lift from The Remains of the Day, in which the stuffy old butler proposes to the starchy old housekeeper. Stone the crows and knock us all down with a feather, Carson popped the question to Mrs Hughes. And what, of all the wonderfully blindsiding things, did she say in reply?

Four years ago Christopher Jefferies was the victim of a concerted attack by the British press. His tenant Joanna Yeates had been murdered and, lacking any other leads, police arrested her landlord. While he was still being questioned, the newspapers sniffed around Jefferies’s patch of Bristol and, armed with a juicy quotation or two, chose collectively to forget all about the principle of innocent until proven otherwise. "Weird", "posh", "lewd", "creepy" were among the epithets in The Sun. He was branded a peeping Tom.

On and on the stately galleon sails. The fifth wodge of Downton Abbey has been light on utter knuckle-gnawing preposterousness. Plots conjured up at random from thin air have been in slightly shorter supply than usual. The very worst you can say of it is that Lord Fellowes is no Agatha Christie. The poor old blighted Bateses have now been subject to a matching pair of cack-handed murder mysteries. To get accidentally banged up once in a slow-moving crime plot may be counted a misfortune. Twice looks like cluelessness.

It takes some brass neck to look at one of the most destructive events in London’s history, which destroyed a chunk of the poorest part of the city and left an estimated 70,000 people homeless, and think that it wasn’t dramatic enough. But that must have been what went through the head of Tom Bradby, the political editor of ITV News, when he was writing his four-part drama: we were deeply immersed in espionage, war, assassination plots, kidnap and a spendthrift, philandering king before as much as a single spark began to fly.

Julian Fellowes, now the Conservative peer Lord Fellowes, left behind the fictional world of Gosford Park and Downton Abbey to give us this sumptuous tour of Blenheim Palace. Nor were its surroundings neglected as vista after vista showed us Blenheim’s lavishly landscaped gardens, fountains and columned monument to John Churchill, ^1st Duke of Marlborough, victorious over Louis XIV. It was his military prowess that led to wealth and Blenheim itself, gifted by the grateful nation and thus an early example of government subsidy.

When Rachel Bailey (Suranne Jones) told the promotion board at the beginning of this series: “I’m not a liability, I’m a safe pair of hands”, we knew it would be a matter of sitting back and waiting to see in what manner she would heap disgrace upon herself.

As unavoidable as death and taxes, as inevitable as the rotation of the seasons, Downton Abbey has created the illusion of time-hallowed permanence in a mere four years. It is often asked how long Julian Fellowes can keep up his script-writing heroics (if it was an American show he'd be marshalling a writing team of dozens), but this opener to series five was so playfully deft and thunderously enjoyable that you'd have to conclude that Downton has become Fellowes's personal fountain of youth.

With Cilla Black still fighting fit and eminently telly-worthy at 71, it feels a bit odd to find a three-part dramatisation of her life popping up on ITV. Black apparently gave the project her blessing and has hailed Sheridan Smith's performance in the title role, but all this does is to tacitly suggest that it's a fairly harmless piece of entertainment which is unlikely to go poking about in any dark or controversial areas. Team Cilla would surely have had the scheme quashed otherwise.