Rather than warehouse work/forklift truck driving, etc. a proper driving job would be more helpful.
Maybe you can work 1 day each week driving a 3.5 tonne supermarket delivery vehicle in addition to your office job. If you do 8 hours at £10/hour you should take home £64 as only 20% income tax will be payable on that and no National Insurance. This is because you don’t pay any NI on the first £184/week on each PAYE payroll that you’re on.