Over the Winter Months, it's doubtful many people think about their air conditioning. So I'm guessing that's why Kwik Fit usually do this offer over the winter!
For £25 (usually £44.95), they replace and recharge lubricant and refrigerant levels in line with your manufacturers recommendation. If they cannot improve the coolest vent temperature from your car by more than 10% when measured in degrees Celsius - then you pay nothing at all.
I'm a skeptic about Kwik Fit. But, for this price for this service it's good value. I highly doubt your ever going to get this free of charge, but there is a chance. But please stick to your guns if you go for it, just go in for your air conditioning. Don't get anything else checked, as they will probably find £100 of work that apparently needs doing to your car.