Last Night's Television - Who Do You Think You Are?, BBC1; Whitechapel, ITV1

Hold the front, or in this case the inside-back page! Unforgiven, the ITV1 drama that finished last week, offered writing and acting out of the very top drawer, and Whitechapel, which started last night, looks to be out of the next drawer down. I hate to cram too many metaphors into one paragraph, but gripping ITV1 dramas are like London buses: you wait for ages, then two come along in rapid succession.

Whitechapel stars Rupert Penry-Jones, last seen legging it through the heather in a slightly clunky version of The 39 Steps, as Joseph Chandler, a high-flying detective inspector with the Metropolitan Police. Chandler's ascent through the ranks, however, owes more to his lofty social connections, and in particular the patronage of the commissioner (Alex Jennings), than any notable record of dirtying his hands with proper police work. On the contrary, DI Chandler hates getting his hands dirty. He is a cleanliness freak, whose neuroses are challenged when he is dispatched to take charge of an investigation into a grisly murder in the East End, partly because grisly murders are by definition messy, but mainly because the detectives he must lead, working out of Whitechapel cop shop, are a slovenly bunch. Naturally, they resent the arrival of Chandler, who as well as being suspiciously clean and tidy is also disconcertingly tall and posh. Small, messy and decidedly unposh Detective Sergeant Miles (the ever-excellent Phil Davis) orchestrates the resentment.

Now, there are problems with all this, for us as well as for them. For us the problem is a wearyingly familiar TV formula, the one that presents the detective as a maverick or misfit, being pitched in with mistrustful and usually unreconstructed new colleagues. In Prime Suspect it was a woman, in Life on Mars it was a time-traveller, and I could fill the rest of this column with further examples going back to the 1970s and beyond. Remember Dennis Weaver's McCloud, the cowboy in New York City? Chandler is McCloud with antiseptic wipes instead of a 10-gallon hat.

The problem for them, meanwhile, is that the clash of personalities impedes the investigation, with the seen-it-all cop Miles refusing to believe that the murder is a precise copy of the first strike by Jack the Ripper, 120 years earlier. Every time there is a murder in Whitechapel, he complained, some "Ripperologist" surfaces to invoke Victorian London. The Ripperologist here is Steve Pemberton from The League of Gentlemen, having a high old time leading tourists along streets almost as creepy as those in Royston Vasey. When he pointed out to Chambers the uncanny similarities with Jack the Ripper's crimes, Chambers believes him. When another woman is murdered in the same way, even Miles grudgingly accepts that their quarry is a copycat serial killer.

None of this brought anything original to what is essentially a standard police procedural (albeit with more gore than we normally get), so why did I enjoy it? Partly it was the acting, by Davis and Pemberton in particular, but mostly it was S J Clarkson's direction, a little over-flashy at times but very good in the crucial business of generating mood and suspense. I even just about forgave the inevitable way in which the background music kept infiltrating the foreground, making it sound as though it wasn't just a murderer loose on the streets of Whitechapel, but also the entire strings section of the London Symphony Orchestra.

From Ripperology to genealogy. A new series of Who Do You Think You Are? kicked off with Rory Bremner, making the title even more apt than usual, although Bremner on the whole held back the impressions, except for the frightfully pukka 1940s English he used to intone the entries in a phrasebook circulated to British Army personnel, including his father, Major Donald Bremner, stationed in Germany after the Second World War. With the high-handedness that the victors doubtless felt was their privilege, most of the phrases were highly peremptory, such as "go away, please. I cannot talk to you now."

Bremner's father was 53 when his younger son was born, and died 18 years later ravaged by cancer. With tragic irony the cancer charity he worked for after leaving the army summarily fired him when he got cancer himself, sending him a signed photograph of the Duke of Devonshire as a leaving present. Bremner dates his own highly productive sense of injustice from that moment.

Some years ago, incidentally, Ken Dodd was a guest on the Radio 4 programme In the Psychiatrist's Chair. Dr Anthony Clare introduced him by saying that he intended to strip away the mask of the clown, get beneath the carapace of the funny man, to see what made him tick. "How," he asked Dodd, "do you feel about that?" To which Dodd replied that he felt it was quite tatttifilarious and totally plumptious. In other words, he had no intention of letting his clown's mask slip. Bremner, by contrast, let us see exactly what makes him tick, another triumph for a series that is never less than watchable, and quite often deeply moving.