'We just checked your Twitter and you're an arse.' Having three audience members stomp out of your show before it's even started is probably something that would only ever happen on the Free Fringe. And maybe it's the kind of thing that only ever happens to Trevor Lock. Either way, he ploughs on largely unperturbed with an hour of chatty improv which seeks to bring a room together while occasionally splitting opinion straight down the middle.

Non-scripted comedy isn't for everyone, but judging by most people's faces here, Lock's occasionally passive-aggressive manner (which from time to time amusingly holds the passive) does hit the mid-afternoon spot. It's easier to actually see what the crowd thinks in a room like this given that our comic has arranged the seating so that it's facing each other while a select number of crowd members (aka latecoming stragglers) are invited to perch on seats around Lock up on his stage.

As you can imagine, housekeeping takes up a sizeable chunk of the introductory preamble, while the remainder has our host dragging as much of his audience into the fray as he can: Lock discovers which people are the oldest and youngest among us, which person should be deemed the 'mother', who should take notes, and which trusted participant can let him know when it's 3pm and then 3.30pm.

On this day, there's an awful lot of back and forth about circumcision (only repeat visitors can attest as to whether this is a regular preoccupation of Lock's, or whether it merely raised its head on this occasion) and when the chaos winds down, he requests applause for those who made valuable contributions. It's always slightly awkward when an audience member gets the biggest laugh in adlibbing affairs like this, but Lock has opened up the possibility that someone else could steal his show. If you want to find out how Trevor Lock gets on with such things as a script, pacing timing, and, you know, jokes, you'll just have to seek him out elsewhere.

Trevor Lock's Show, Bannermans, until Sunday 29 August (not Saturday 28), various times; Whistlebinkies, Saturday 28 August, 2.45pm, Pay What You Can.