Terra Nova, Monday, Sky 1<br/>Mary Queen of Frocks, Tuesday, Channel 4

It was meant to be the T. rex of telly. With a monstrous budget of a reported $70m (£46m), the Steven Spielberg-produced sci-fi series Terra Nova has broken records for most expensive show of all time.

It's 2149, and man has trashed the planet. We're introduced to this polluted dystopia through predictable CGI swoopery; it's both grubbily grey and glittering with electric lights (although the cramped interiors just look like the ultimate in Ikea "storage solutions").

Humanity's future now lies in, well, the past. Thanks to some sci-fi cleverness, we can travel back to the cretaceous period, although why this particular, dinosaur-ridden epoch is chosen is unclear. Anyway, we follow the Shannon family through a portal and back to prehistoric paradise, where there's another CGI frenzy of abundant waterfalls and lush forests.

There's some drama in the getting there: maverick cop dad Jim Shannon (Jason O'Mara) has to break out of prison; he and wife Elisabeth (Shelley Conn) hadn't been so good at keeping to the two-children-only population law. And their teenage son is angsty about leaving his girlfriend – until he meets a feisty young thing on arrival, anyway.

But the hope is that this is where the drama really kicks off: because here be dinosaurs. Yet aside from a little hand-feeding over the gates of their camp (think primeval Butlins meets luxury eco-cabins), the first episode is curiously unsatisfying. Apparently, Hollywood scriptwriters were drafted in to give more "heart" to the story, focusing on family dynamics. Given the script's clunking predictability – "He'll make it. He has to." – their £20,000-a-week wordsmithery wasn't good value.

The second episode, immediately following the first on Sky1, was more fun. Jim got to show his irrepressible tough-cop nature when some rebels showed up, and the dinosaurs got all Jurassic Park, attempting to chow down on the juicy young flesh of the teenagers who had rebelliously snuck out of camp. While the plotting and dialogue remained woeful, at least the tension was ramped up as big-toothed, hungry dinosaurs encountered dumb teens in hotpants.

The latest venture of shopping guru Mary Portas was inspired by a reluctance to dress like said posterior-exhibiting teens. Convinced there's a glaring gap in the market for the over-40, but not over-the-hill, woman who doesn't want to look like either "a whore or a granny", the Queen of Shops decided to open her own.

As Peter, her "long-suffering business partner", points out in Mary Queen of Frocks: "There's going to be a lot of people gunning for it not to succeed." Having made a career of telling others where they're going wrong, if Portas shows an inch of vulnerable flesh, she and her shop are likely to be ripped apart. Luckily, she seems to have a full-body suit of armour forged of extreme self-confidence; Portas's mantra is "I know what women want!" interspersed with bellowing "I know this is a great idea!" She is incredulous when M&S's boss won't return her calls, or when only one person applies to work in the 2,000sq ft of House of Fraser she is eventually given to open up shop in.

Of course, this being a TV show there has to be a "journey" (she even yuckily refers to it as such) so we are shown stressful meetings, anguished cab rides and teary moments. Generally, though, Portas has bags of enthusiasm and seems honestly eager to see the best in people. Her insistence on having "happy" staff is a tad patronising, mind; having held down a similar sort of sales job, I've more sympathy with bored assistants failing to hype a hemline than Portas's army of passionate product pushers. Just how exciting can a structured jacket be?

Portas's project may not be dealing in the same number of noughts as Terra Nova, but she is expected to shift £2m in her first year. Yet something tells me even a dinosaur in her path wouldn't stop Portas pursuing that Queen of Frocks crown.