When you enter prison you will be asked to sign a work agreement. If you sign it and fail to get work you will receive £2.50 per week in unemployment pay. If you refuse to sign you will get nothing and it could prevent you progressing to a lower category prison.
Assuming that you are prepared to work you will be called before the Work Board. Ensure that the Board is aware of any health reason why you cannot do certain types of work. In those Prisons where outside work is provided eg farming, you might feel that you would prefer to be ill. Mucking out in the middle of winter at 6am for £1.11 per day is hardly a good idea.
Work done in prisons for the service itself ranges from filling polythene bags with tea, coffee and sugar sachets to making clothing and shoes to farming. In addition the Prison Service takes on outside contracts such as filling those same polythene bags with tea, coffee and sugar sachets, but this time for British Airways or folding yellow sacks and letters for clothes collecting charities.
Pay is determined by the local Governor but it is usually around £1.50 per day. Some Prisons actually organise work on a piece rate which means if you don't manage to fill the required number of bags you get nothing. One prisoner I spoke to actually got less than he would have done on unemployment pay because he had been given the wrong sachets to fill the bags with. He complained but it was his fault so he did not win. Strangely some prisons actually pay £2.50 per day for less onerous work than the farm work at £1.11 per day.
Other work that is available in open prisons is outside the prison and realistic rates of pay are provided but still much less than the National Minimum Wage.
Good jobs in prisons tend to be cleaners, librarians, cooks, orderlies, servery. These will all get you out of your cell for longer and the amount of work to be done is usually quite small.