Alison Graham

Only Graham Norton could ever come up with such an eclectic range of guests - global megastar Lady Gaga, actor Jude Law, comedian Greg Davies and EastEnders' Dot Branning (or rather the actress who plays her, June Brown). Who will flirt with whom, we wonder?

Lady Gaga was on the show back in 2011, dressed in an extraordinary Bride of Frankenstein-type outfit. She was last spotted in a fur mask with a gold beak on a tour to promote her new album. Tabloid favourite Law talks about his new gangster film Dom Hemingway, Davies's current sitcom Man Down (9.30pm C4) is winning him laughs and acclaim, while Brown discusses her autobiography.

A flinty government vetting officer turns up at the British Embassy in Tazbekistan. He's so tough he walked from the airport 15 miles away and is barely perturbed by the fact that the country is in the grip of revolution.

As the power fails and shots ring through the night air, British ambassador Keith Davis and his deputy Neil Tilly (David Mitchell and Robert Webb) have to think on their feet. Someone has to suck up to the president's monstrous daughter, a primped, plastic surgery-obsessed brute with her own wine label; while Keith has to make peace with the insurgents, though they are late for a rendezvous: "You can't expect punctuality from rebels," he says with true British grit. "They are rebels, aren't they?"

It's been an engaging series; I hope it returns.

Poor, hapless Alan Davies is on the receiving end of a storm of QI klaxons as he good-naturedly lurches from one wrong answer to the next. But it's an honourable tradition and Davies is a willing fallguy - he even fails at a supposedly foolproof experiment involving a broom's centre of gravity.

Elsewhere, guests Danny Baker, Jo Brand and Marcus Brigstocke enjoy a bit of a jolly knockabout that's full of surprises and "well, I never knew that" sort of facts, including the answer to questions such as £what do mosquitos do in the rain?" and which country has the longest traffic jams. At one point it all becomes a bit much for Baker who wails, "On behalf of the audience I have to say, sometimes I hate this programme."

While Jonathan Ross had to content himself interviewing stars of an ITV show last Saturday (the X Factor judges), Norton once again lures some global, glittery names on to his sofa.

His old mate, the indefatigable Sir Elton John, will perform Voyeur and be interviewed fresh from the triumphant release of his well-received 31st studio album, The Diving Board. He'll be joined by the mighty Dame Judi Dench, whose name is already being mentioned in the same breath as "Oscar nomination" for her role in the new film Philomena, as an Irish mother searching for the child she was forced to give up for adoption. Ever reliable John Bishop will be in the comedy corner.

The British Embassy in Tazbekistan prepares for the arrival of Prince Mark, a trade envoy and minor member of the royal family. He turns out to be a spoilt, entitled berk (a great comic turn from Tom Hollander) who travels everywhere with a 6ft ironing board so his factotum can ensure the creases in the Prince's trousers are perfect.

Though Ambassadors feels a shade underwritten and falls uncomfortably between drama and comedy (that tricky middle ground is always a hard place to sit), it bowls along thanks to a sharp cast - David Mitchell and Robert Webb play the ambassador and his capable deputy, and there's a great foul-mouthed cameo from Matthew Macfadyen as their furious government boss.

And Frasier fans, watch out for Edward Hibbert (restaurant critic Gil Chesterton) as an equerry.

It's good to see David Mitchell and Robert Webb back together on television, though Ambassadors is more Graham Greene than it is Peep Show. There are some funny bits, but it's a drama with a light touch, rather than an out-and-out comedy. Not that there's anything wrong with that, as this is an engaging, even winning, hour. Mitchell is Keith Davis, Britain's new ambassador to Tazbekistan, a (fictional) central Asian country with a terrible human rights record. His highly capable deputy is Neil Tilly (Webb), a man with a private life that could turn out to be his downfall.

The well-meaning Davis has to secure a huge Tazbekistan order for British helicopters and hopes that a limp Best of Britain-themed party, including a one-man version of Frankenstein performed by a preposterously pretentious actor, might do the trick.

That cranky carapace cracks just a little as the Doc faces the repercussions of the painful events in the last episode. His marriage looks wounded beyond repair and he's stuck at home in pretty Portwenn with only his ghastly, grasping, emotionally exploitative mother for company.

It's the final episode and, as Doc Martin has never been a series that would ever willingly give in to the fervent hopes of its devoted audience (just think how long it took Martin and Louisa to marry) fans must brace themselves. Pour a stiff drink, find some worry beads and prepare to hold the hand, mentally, of this most difficult of men. He needs your support.

Martin Clunes is great as Martin and, even if you're ambivalent about the appeal of his flinty personality, you'll need a heart of concrete not to feel his every flinch of pain in an unexpectedly touching finale.

The mighty Graham Norton returned to his Friday night chat-berth last week, when he was greeted with open arms by viewers, and tonight the slightly less mighty Ross is back. The unspoken but received wisdom is that Norton gets the good guests, but the opening show is stellar. Tom Hanks is the guest everyone wants because he's a pro - easy-going, effortlessly funny, he knows what's required of him and he delivers. He'' with Ross tonight to talk about his new film Captain Phillips, based on the true story of the hijacking of a ship by Somali pirates. The word "Oscar" is already being bandied about. Fellow guest Sandra Bullock could be up for glittering prizes too with her new film Gravity, about stranded astronauts.

The Doc's blood phobia is getting worse, as is his consequent insomnia, which is also beginning to disturb his wife Louisa in the marital bed. Maybe it's time he saw that psychologist his Aunty Ruth recommended, particularly when there's an unfortunate and very public incident involving Doc Martin, dopey police officer Penhale and a staple-gun. Penhale (John Marquez) causes widespread panic in Portwenn after jumping to conclusions about an asbestos scare.

But nothing is quite as terrifying as the sight of Martin's poised, chilly mother (played by Claire Bloom) who turns up on his doorstep with some news which, if delivered to any sentient human being other than Martin (Martin Clunes) being would be cause for thoughtfulness and sadness. But not the blithely unempathetic Doc, oh no. Not in a million years.

Portwenn is agog - Mrs Tishell, the overwrought pharmacist in a neckbrace whose morbid sexual obsession with Doc Martin led her to kidnap his baby son, is back in the village. She's still in a neckbrace, but, apart from worrying an elastic band around her wrist (part of her treatment) she seems reformed and contrite. Louisa and Martin, though, aren't so sure.

This series has exercised even die-hard fans, if RT's letters page is anything to go by, with grumblings particularly about its lame farcical elements. There's more damp comedy tonight in a couple of those Doc Martin sub-plots that can barely summon the energy to lift their heads from the pillow - dim PC Penhale goes all Bear Grylls on a survival exercise, and Al tries internet dating. You won't need a map to follow where the stories lead... Meanwhile, Bert tries his luck with a lady.