There are multiple approaches you could take here. The problem is that finding something which is "quick money" but also good money. Here's my experience:
For the record, I've done £200 /hour consulting, I've owned businesses that employed teams, I've sold phone call consulting, I've written and sold a book, I've done paid speaking gigs, paid teaching gigs....and I've also sold laptops for £7 /hr.
Some were big money, some were quick money, few were both.
If your core expertise and career goal is a knowledge worker (you're a great strategy consultant or web developer) then most revenue opportunities will need a little time to ramp up. Writing a book, or getting consulting gigs (and getting paid) all takes weeks or months.
This is because you either need to create the product (and create the marketing buzz and audience around it) or you need to invest time to build up a portfolio, reputation, testimonials, networks and contacts.
But once they're up and running, a book can easily bring in £1,000 per month with only 4 hours work a week writing blog posts and emails to promote it. Just 2 days consulting at £500-£750 /day could pay the rent and bills for a full month.
So writing just 1 book, or doing just a couple days a month, could be the difference between survival or not.
However, in my life I've had times when I needed something *now*. A bill came up. The credit card was maxed. Whatever - life said "Hey, you messed up cashflow this month!".
And so I've put my ego aside and ignored the fact that I can write code for £300 /day or I can do consulting for £500 /day.... and I've gone to work for a nighclub promotions team for £100 /night. Cash paid, there and then, money was in my pocket.
I also have a friend who's on a sweet salary, university educated, gets great consulting work... but sometimes when something bites her in the ass, she'll jump into doing some cleaning shifts with an agency for £10 per hour. Despite selling her copywriting to PR agencies in London for £100 /hr.
So yeah, I guess I'm trying to say explore how to monetize and productize your expertise. But if you need something fast and short term, there are many legal ways to make "quick cash" that usually require nothing more than swallowing some pride and focussing on the end goal to get you through.