There are courses available for adults with low literacy and numeracy skills. Most colleges in most towns have basic entry level lit/num courses, and most are free too.
Wether they are widely advertised and easy to access is another thing, but they are available.
I come acorss many adult men who have such problems with literacy and numeracy, especialy literacy. In the prison most of our men have literacy levels of entry level 3 and below. This means most of our prisoners (in my prison anyway) work at no higher than an 11 year olds level. Many are far below this, and some are unable to read/write at all, with no letter sound awareness even.
We have a policy of having all prisoners work towards adult literacy level 2, which is what the Government see as the required working level for an adult in the UK. We have fully qualified and trained teachers to deliver this. However we can not enforce the requirement to do the classes, and many chose not to address their literacy skills at all. But it is lovely to see those that do give it a go and succeed, very warming.