More than one in five Sussex residents lacks basic education skills, according to a worrying new report.
A TUC survey of the South-East shows the county has some of the worst literacy and numeracy rates in the region.
According Anthony Dunnett, chief executive of the South-East England Development Agency (Seeda), those lacking skills would have trouble reading Health and Safety notices at work or counting their change in shops.
Three districts of the county, Rother, Eastbourne and Arun, appear in the bottom five places of the report.
Also low on the table are Crawley, Hastings, Worthing, Adur and Lewes. Only Mid Sussex appears in the region's top 30 districts.
The figures show a total of 180,080 Sussex residents have trouble reading and writing, while 170,221 have problems with numbers.
In Sussex, Rother comes last. In that area more than a quarter of the population suffer from poor literacy. Crawley was the worst place for numeracy, where 25.8 per cent of people have problems with numbers.
The report, published next Monday, says low aspirations, unemployment, low skill levels and low productivity contribute to the problems.
Barry Francis, regional co-ordinator for TUC Learning in the South-East, said: "It is a big problem that can have repercussions on productivity.
"The problem has now been recognised and people are beginning to deal with it but there is a lot more room for improvement."
Despite the grim figures, there are some encouraging signs for adult learning in the county.
The report singles out a partnership in Brighton and Hove, between Seeda and the city's street cleaners, as a good example of unions and employers promoting adult learning.
Mr Francis said other employers, like South Central trains and the Inland Revenue, were also helping to develop employees' skills.
He said such initiatives helped remove the "stigma" attached to problems with literacy and numeracy.
Mr Dunnett said his agency was the only one in the country that was running programmes to improve the literacy and numeracy of people already in work.
He said, despite the affluent image of the region, the levels of skills deprivation here are as high as anywhere else in the UK.
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