The Secret Policeman's Ball, Royal Albert Hall, London <!-- none onestar twostar threestar fourstar fivestar -->

"I've had the best evening of my life watching this," said the actor Jeremy Irons as he closed the fifth Secret Policeman's Ball in 27 years. It was the kind of emotional assessment that could only come after a marathon session of entertainment and a resonant demonstration of the task that Amnesty International has set itself. In truth, it was a decent charity gig, which had inevitable peaks and troughs. The four-hour revue spanned such diverse acts as The Mighty Boosh and their pantomime antics, and the understated whimsy of Dylan Moran.

The Royal Albert Hall was filled with 5,000 expectant punters, so every silence or duff gag was amplified to the maximum. The order of the acts was crucial to the building of momentum. In this respect, the aforementioned Moran suffered by being put in the headline slot. He was on good form, but his quiet charm didn't generate the warmth that his cute observations (such as the US invading a country by surreptitiously building a Starbucks around the population) deserved.

Proceedings weren't much helped by a staccato sketch about Guantanamo Bay by the US comedy icon Chevy Chase. He seemed slow on his cues and, frankly, didn't do his talent justice in this rare UK appearance. Meanwhile, Brits pretending to be Yanks - Julia Davis and Jessica Stevenson - subsequently served up a passable country-and-western pastiche. It was spattered with some jolly innuendoes, but it was ultimately dwarfed by the vastness of the main stage.

Enter Andrew Maxwell, the show's "unknown" package. I have championed the Irishman in the past, and I suspect that, after tonight, he may well have an additional 4,999 supporters. Maxwell briefly became the MC for the evening (the gig needed one badly), and whipped up the crowd with some good-natured audience participation and a number of routines, including a Robin Williamsesque one about how women should rule the world because they're good at clearing up after men.

The evening was on a high by this point. A skit by Jimmy Fallon, the US Saturday Night Live star, and another involving Graham Norton, Jon Culshaw and Ronni Ancona (whose Jennifer Saunders impression compensated for the absence of the real thing) passed well enough.

Russell Brand then upped the ante again on the second stage, which was in the shape of Amnesty's logo and was where most of the stand-up took place. His hairdo was even more bouffant than usual, and he laid into The Sun, his favourite hobby horse, which he personified as your cockney mate who has racist views and who keeps you on side with cheap offers for booze cruises.

After Brand, there was a "Russell Brand impersonator", or so went the insult hurled at Noel Fielding by his comedy partner, Julian Barratt, who are known collectively as The Mighty Boosh. Their double act received a welcoming roar, as if they were a rock band. Their fey ways and and harmless fumblings weren't hilarious, but they made sweet music and were undeniably charming.

The second half of the show lacked the rhythm of the first. Al Murray as The Pub Landlord served up a solid performance, which provided no surprises for anyone who had seen him before; some of the cast of Green Wing, Channel 4's hospital-based comedy, delivered a sketch more painful than MRSA; Omid Djalili bravely attempted to send up dictators; and then there was the ubiquitous ensemble piece - a Cluedo murder- mystery - in which everyone (including Richard E Grant and Jo Brand) went down together.

Eddie Izzard was only moderately entertaining with a business-as-usual routine about flies. Then there was the top American comic Sarah Silverman, whose sweet but slightly chilly persona didn't prepare us for her forays into bad taste ("I needed some good news today - so I got an Aids test").

But the evening was about causes first and comedy second. And if some of these performers were unleashed on a new audience and picked up a few fans along the way, it was no more than they deserved for their participation in a fitfully arresting evening.