I did this about 3 years ago! I got fed up and could never risk fully starting up on my own due to commitments.
Write ups will do you the world of good, suddenly you'll find yourself with people being impressed and asking for work.
There was a time where I took holiday from work to do detailing it was that busy. You've started very different to me mind, you've probably gone the better way by going trade!
You can build up to an enhancement detail every day and charge £100! 5 days a week, £500, £2000 a month! Take taxes, travelling, products out of the equation and probably 1500 a month which is a decent wage!
One bit of advice to keep costs down is look at trade suppliers such as autosmart! They can help keep costs down and drive your profits up!
I'll post some links of where You can find my work and see how people comment and request work when they see step by step write ups!