The Thick of It, BBC2, Saturday Mrs Biggs, ITV1, Wednesday The Bletchley Circle, ITV1, Thursday Dallas, Channel 5, Wednesday

An equalities minister who has voted against racial and sexual equality rights. Chuckle. A health secretary who supports homeopathy. Ha! It's good, this politics malarkey, isn't it? A right giggle. Some might think it beyond parody. But thankfully not the Thick of It crew, who, three years after its last series, returned last night with an eagerly awaited fourth to take on the calamity coalition.

First, the good. In fact, the excellent. Roger Allam as the Tory MP Peter Mannion, new head of Dosac – the Department of Social Affairs and Citizenship – fills the role perfectly. The floppy hair, the floundering as he tried to explain a "networked nation" that was beyond him, the barely concealed contempt for those he works with ("I'm bored of this," he said, walking out of a meeting with his junior minister. "I'm going for a Twix") and those he works for. ("I hate schoolchildren. They don't even have the vote. Might as well talk to fucking geese.")

Then there's the spin doctor Stewart Pearson, a lighter touch than attack dog Malcolm Tucker, all herbal teas, brainstorming and, in the words of Mannion aide Phil Smith, provider of "seven years of ear piss".

That Tories and Lib Dems might not get on behind closed doors has been the subject of satire ever since this bastard child of Westminster was conceived in May 2010, but it was moved on here to good effect. It reveals the flaws in the central characters and allows for the best line of the night, uttered by Ben Willbond as Lib Dem No 2 Adam Kenyon. "Landmark day," he said as Mannion finally destroyed the launch of the Liberals' "silicon playgrounds". "We bring in an idea, you like it, you nick it, you put two bullets in the back of its head. Snuff politics: you've got to laugh." And you did, you really did.

Yet not everything was quite so sparkling. Punchlines were occasionally heavy-handed and the ranting felt sometimes forced. Consider Lib Dem junior minister Fergus Williams's tirade at punchbag press officer Terri Coverley: "Now you like musicals. Well this is 'Tonight' from West Side Story, and I'm going to bring the bloody house down, so you can't rain on my parade, Funny Girl." Too contrived. Maybe that was the point, but it made you pine for the eloquent misanthropy of Peter Capaldi's expletive-fuelled Tucker. Luckily, he's back in episode two…

ITV1 came big with the historical drama last week, bringing us Mrs Biggs and The Bletchley Circle. In the former, Ronnie – of Great Train Robbery fame – was played by Daniel Mays as a lovable, though not entirely charismatic, rogue. It made you wonder why Charmian, the Mrs of the title, promised to stand by him for ever when the best he'd done was be a cheeky lad.

The episode seemed set up so he could blame her for his part in travel's most famous crime because she wanted a bigger house. It got a bit panto at times, particularly the portrayal of Bruce, the mastermind behind the robbery. The biggest mystery was why it was called Mrs Biggs at all. Other than walking out on her stentorian father, she didn't really drive any of the action, and anything she did do (steal from her boss, run away from home, go back home) was forced on her by the men in her life.

Bletchley, meanwhile, told the story of four fictional women who helped to end the Second World War with their superior puzzle-cracking and feats of memory. They've returned to "normal life" in the 1950s – ironing, doing the washing, working in a library – only there's a serial killer on the loose and Susan (speciality: crosswords) was determined to find him before he can kill again.

Anna Maxwell Martin was superb as the lead, but her co-stars, including the normally excellent Rachael Stirling and Julie Graham, were not given enough to do. And while the core conceit was neat (though I have to admit to getting lost when they were working out how to catch the murderer by synthesising train timetables), the execution felt a bit Agatha Christie by way of The Bill.

Talking of dodgy old soaps, Dallas is back! Look, there are the high-rise buildings! And some cows! And more buildings! And more cows! And that three-way split-screen! How exciting! But once we were into the action, I remembered why I used to be bored by Dallas. Yes, there were power struggles and they've thrown a bit of international relations in for good measure, with brief mention of Chinese oil interests. But essentially it's still just a series of slappings, slap and tickle, back-slappings and backstabbings, only this time J R seemed to be playing it for smiles and Sue Ellen (who, weirdly, doesn't appear to have aged) didn't have so much as a snifter of booze. Boo!

The new generation was all very pretty, and pretty vacant, and there was some guff about earthquake tremors (fracking hell) and alternative energies. But, frankly, until J R awoke from his catatonic state (probably bored by everyone else on the ranch), it wasn't worth diddly squat. Still, if the writers promise to give a bit more menace to 10-gallon Larry, I might catch up with the folks at Southfork next week – if only to hum along to that theme tune.