At college it works out about £950 - £1000 monthly all in with housing allowance and after tax.
After being posted (assuming you get through with no retakes) which is about 4/5 months for a London Airport (TWR only), 9 months for other airports (TWR + APR) or TC (APR only) or just under a year for area, pay goes up to £15k (band 1) to £18k (band 5) but you lose the housing allowance, so it works out about the same.
My pay actually went down after being posted as I pay into my pension now which makes a difference.