There is a lot available free. My wife delivers many courses that "Embed" basic skills into other subjects.
Yes I do remember CSEs. In fact GCSEs are supposed to be a combination of GCE 'O' Levels and CSEs ~ Tho' I confess I hadn't realised you were that old.
Joking apart demonstrating that you are working towards acquiring the skills or at least proof of them will enhance your prospects and get the Job Centre Jobsworths off your neck for quite some time.
Check out your local FE College for courses starting in September ~ they will offer Basic Numeracy and Literacy and you can work your way up through the levels ~ before you feel insulted my wife has 10 O Levels, 6 "Highers" (they are Scottish A levels) a BA(Hons) in Humanities + Dip Euro Hum + a PGCE BUT because her O and A levels are now more than two years old had to attend a local college to take the basic Literacy and Numeracy Courses and tests, despite having passed the two year PGCE course with Honours, before they would award her the PGCE (Post Graduate Certificate of Education ~ meaning she is now a qualified teacher) She is now attending Uni part time again to gain her Masters in Education and plans to do a Phd after that.
The basic Numeracy and Literacy courses are designed for everyone and you can work up the levels at your own speed by attending your local college for a couple of hours a week. They have the added advantage of being computer based and virtually free to those who qualify financially, which I suspect you will. If you attain (and here I am not absolutely sure of the figures) level three it is equivalent to an NVQ but your college will be able to tell you that ~ or Google the info. When Mrs S went along to do hers the tutor told her to p*ss off out of the class as she was putting the others off by being so bright and to come back and sit the tests at the end of the course ~ So even teachers have to take these qualifications under Nu labour because so many of them have not got the basic skills or at least up to date proof of them. (Yes three of those in her class were teachers, One was a Nurse and the rest trainee Classroom Assistants)
Give it a shot and bloody good luck to you. It is the right way to go.