Thanks for the comprehensive answers.
We can manage on such a low income (just) but I wouldn't be able to overpay on debt. However we would be debt clear end of 2020 if we stick to the budget. Potentially quicker as I often make an extra £200 -£300 a month but that is an adhoc thing and not guaranteed.
Assuming that the outdoor instructor thing is a done deal (have you considered OH delaying it for a year to try to get higher paid work without the qualification?), I would save a chunky emergency fund (or keep it if you already have one after paying off the high interest loan) and plough the rest into the debt repayment. Do OH's earnings after getting the qualification make it financially worthwhile in the long run?
Start living on the 'new' budget now so that you test that it is accurate and can make the most informed choice. Would there be additional costs for the training year that you don't pay now (childcare, travel?)? Your e-fund should be for unforeseen issues (time between jobs, major appliance breakdown) rather than supplementing day to day living IMO. If you couldn't afford to live during the outdoors course then now probably isn't the right time to do it.
It's a shame about the car lease, but never mind. I'm in total agreement about the student loans - I'd be gutted if I paid them off early and then something terrible happened and I couldn't work again. Or even if I paid them off and then got to the age that they'd be written off and realised that I'd given the government extra tax for no reason!
I'm sure you know this because you seem totally on top of things, but make absolutely sure the minimum payments are going through on the cards. I had an issue where the direct debit for a new card failed, the Financial Ombudsman intervened and told the new card company that it was their fault and they needed to sort it out but loads of my credit limits were reduced before I even knew there was a problem and it was a nightmare getting them back. This was over a year ago and my credit score is still ~200 points lower than it used to be.