Rough numbers here, but I'm figuring that to warrant a loss in the £430k annual revenue from the development fee, they would need as a minimum of 215k departing passengers with a fee of £2 each.. At this rate there would be very marginal extra costs, increased car park revenue and increased shopping in the outlets in the terminal, sustaining these and potentially driving airport revenue.
215k passengers would require a minimum of 3 daily departures...and prob a bit more. What's the chance of x2 daily STN, daily GLA and MAN... On most days and a seasonal but limited selection on sun routes ALC, FAO and AGP?