When he was chair of the judges for the Man Booker Prize in 2008, Michael Portillo presided over the exclusion from the shortlist of such heavyweights as Salman Rushdie and Joseph O'Neill. He confided at the time that there had been "passionate", not to say heated, debate among the judges.

The signs are that the deliberations of the judging panel for this year's Art Fund Prize for museums and galleries, which Portillo is also chairing, have been conducted at a rather lower temperature. "There's been a huge amount of enlightenment," he tells me, "but not heat. Yesterday, we talked about the shortlist and had the most wonderful discussion."

Portillo and his fellow judges - the scientist Jim al-Khalili, the artist Jeremy Deller, the journalist Charlotte Higgins, the museums consultant Kathy Gee, the historian and broadcaster Lars Tharp and the crossbench peer Lola Young - are due to announce a shortlist of four museums on 19 May (the winner will be announced on 15 June and will collect a bounty of £100,000). They will be choosing from a longlist of ten, including institutions as different in scale and ambition as the British Museum and Hertford Museum, whose prized possession is a collection of 6,000 toothbrushes.

For Portillo, that variety (and the wide geographical spread) is the longlist's main strength. "We were looking for things like innovation, flair and engagement," he says. "Did you make a transformation? Did you move up a gear? And you can apply [those criteria] on any scale."

Portillo is fluent in modern curatorialese - museums, he argues, need to be interactive and to cultivate "public engagement" - but he rejects the suggestion that in chasing the chimera of "accessibility", museums have sacrificed scholarly rigour. "They use a different language these days: most museums talk about objects and the 'stories' they tell, but I don't think that's a dumbing down."

Indeed, he thinks we might even be living in a golden age of the museum. "I was struck by the optimism that our longlisted museums expressed. They seemed pretty confident they would get through the hard times." Let's hope he's right. l